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Hydroponics Frequently Asked Questions

Hydroponics ›

Growing Methods ›

Growing Media ›

Nutrients & Additives ›

Propagation ›

Lighting ›

Ventilation ›

PH & EC ›

Pests & Plant Health ›


What is hydroponics?

Hydroponics is quite simply a method of growing plants without any soil, instead an inert (chemically inactive, no nutritional content) growing media is used to replace the soil and the plants are supplied regularly with a nutrient rich solution.

Is hydroponics easy?

Hydroponics can be easy if a few basic rules are followed. Always design your growroom first and consider everything you can think of before you start building it. Once designed and built run your growroom with no plants for a few days to make sure everything is ok, (all timing equipment works and ventilation is adequate for lighting). Make sure you have set up your hydroponic growing system correctly that you have chosen and that you are able to supply your garden with good clean water regularly. Once everything has been checked and is ok you can put your plants into your system. Keep things simple to begin with by using a one part nutrient until you have the hang of things a bit more and can then experiment with a two or three part nutrient, follow the guidelines given for the nutrients and as a rule try to lower the amounts used slightly as the amounts given as a guide can sometimes be quite high, well the more you use the more you buy. Many beginners to hydroponics will assume that the more nutrients and boosts they put into the water the better they will do. If you exceed the recommended levels given you will probably over feed your plants and cause yourself much unwanted confusion. With hydroponics an easy way for you to remember what your plants need is the term "LAWN", meaning light, air, water and nutrients, if these are all supplied to your plants correctly and as needed, you won't go far wrong.

What is quicker and better, hydroponics or soil?

Hydroponics produces much quicker growth rates and much better yields, compared to soil grown plants. Hydroponics growing systems and media offer a lot more available oxygen to the roots of the plants producing much quicker growth, and hydroponic systems also deliver water and nutrients directly to the roots of the plants, allowing the plants to put all their energy into the top growth. This is why a hydroponically grown plant, grown for the same amount of time as a soil grown plant, can be much bigger and better, with more yield.

Can I grow anything with hydroponics?

Any plant that grows only roots below the ground surface and develops flowers, fruits and vegetables above can be grown with hydroponics. Hydroponics does have its restrictions with plants that grow and develop fruits or vegetables below the ground surface, these types of plants would require soil or coco coir to be used and not hydroponics..

Growing Methods

What is a Run to Waste System?

A run to waste hydroponic growing system will pump and deliver the stored water and nutrients through pipes and into the growing media to feed the plants and the excess nutrient solution that drains from the growing media will be directed away through pipes and run to waste into another tank or drain, allowing the plants to receive a fresh feed of nutrient solution every time.

What is a Recirculating System?

A recirculating hydroponic growing system will pump and deliver the stored water and nutrients through pipes and into the growing media to feed the plants and the excess nutrient solution that drains from the growing media will be directed back into the main tank, constantly re-circulating the solution in the system.

What is a Passive System?

A passive hydroponics growing system uses capillary action to draw water and nutrients into the media to feed your plants.

What is an Active System?

An active hydroponic system requires a pump or components to actively move the stored water and nutrients around the system to feed your plants.

What is a Flood & Drain / Ebb & Flow?

Flood and drain systems are normally made from pots or trays and use clay pebbles for the main growing media. An irrigation delivery system will pump and flood the pots or trays with water and nutrients covering the growing media and plant roots. When the pump turns off all the water and nutrients will drain or be pumped back into the main storage tank, draining all the growing media and roots of the solution and drawing in loads of fresh oxygen into the media for your plant roots to absorb.

What is Nutrient Film Technique (NFT)?

Nutrient film technique systems support plants on a top tray. Plants are grown in Rockwool blocks or mesh pots and placed into the trays when roots have emerged. Water and nutrients are stored in a main tank and are pumped up through a tube and into the top tray to cover it with a film of nutrient solution. A slight angle is provided to allow the solution to run across the top tray and cover all the plant roots. The excess solution is re-circulated and directed back into the main storage tank.

What is Deep Water Culture (DWC)?

A favourite with many, DWC systems are very easy to use and deliver great results with ease. Water and nutrients are stored in a main tank or pot with an air stone inside to provide a constant supply of bubbles into the solution. Plants are normally grown and supported in mesh pots in the top of the system allowing the roots to be suspended below in the dark chamber full of highly oxygenated nutrient solution. Normally roots would rot off being submerged permanently into water, but with the supply of bubbles everywhere they flourish

What is a Top Feed Drip System?

Top feed drip systems will pump and deliver water and nutrients through irrigation fittings and pipes to the top surface of your growing media in your pots or slabs and allow gravity to pull the solution through the media to feed your plants, excess solution can be re-circulated or run to waste. These systems can be made with a few irrigation fittings and pipe, all available at GreenSea.

What is Vertical Growing?

Vertical growing is quite amazing as it requires less lighting and floor space to be used and it can deliver greater yields. Vertical systems are designed to support your plants vertically around the lights that are positioned central in a vertical position as well. This allows many more plants to be grown in these systems to provide better yields from your crops. Plants would only be grown for a short period to establish their roots in the system and then switched over to their flowering period, as plants are only grown for a few days it enables many more crops per year to be produced in these types of growing systems. Water and nutrients are stored in a main tank and pumped when required to the top of the growing media (usually slabs) to feed your plants, excess solution will re-circulate and be directed back into the main tank.

What is Aeroponics?

Aeroponics is a method of growing plants that are supported in the top of a growing system usually in mesh pots and the roots are suspended below inside the dark chamber. Sprinklers or misters deliver water and nutrients into the chamber to feed your plant roots and excess nutrient solution will drain and return to the main tank. Aeroponics is a most efficient way to grow requiring very little growing media to be used and also nutrients as they are supplied directly to the plant roots.

Growing Media

Why should i pre-soak rockwool prior to using it?

Rockwool fibres are slightly alkaline and would not be suitable for planting into without lowering the PH value first. Soaking Rockwool in an acidic solution with a PH value of about 5.5 for 12 - 24 hours will lower the PH value in the fibres and make them suitable for planting into and placing into your hydroponic system.

Why has my growing media turned green on top?

This is normally caused from over watering your growing media and light penetrating the wet surface this tends to leave a green matter growing on top of your media. The best remedy is to purchase some Block Clean ready to use spray and lightly cover the infected top surfaces, leave for a little while and repeat the application this should remove all green matter from the top surface of your growing media. Try to water a little less and if possible cover the media with some sheet until your plant canopy has developed and covers the media from the intense light in your growroom.

What is Coco coir?

Coco coir is a growing media that has become very popular around the world with many growers in recent years, a good quality growing media for indoor gardening. Coco coir is a light brown fibre made from the outer husks of coconuts, it's chopped into small fine pieces and wash and buffered ready for planting. Coco has a great ability to hold water and is a reliable method for plant cultivation. Growing with coco requires a specific nutrient to be used that is designed for coco cultivation, normally in a two-part formula.

Can I use clay pebbles more than once?

Yes, clay pebbles can be used up to a maximum of three times, after this they can become very brittle and break down very easily. Be sure to clean them well if using them again.

Can I make highly fertilized soil for my seeds or cuttings?

No, it's best not to use a highly fertilised soil as seedlings and cuttings will require very little nutrients to begin, plants will start to require higher nutrient levels when they are in their vegetative or flowering period. Choose a lightly fertilised soil for seeds or cuttings and when re-potting your established plants you can use a highly fertilised soil.

Nutrients & Additives

How do I know if I have hard or soft water?

The easiest way to determine if you have hard or soft water is to look inside your kettle and see if you have any white scale inside. If you do you have white scale you are living in a hard water area. If you don't have white scale and the kettle looks fairly clean inside then you are living in a soft water area. This will help you to order the correct nutrients if you choose one that is available in a hard or soft water formula.

What's better: A one or two part nutrient?

We have used many one-part nutrients and two part nutrients over the years and have to say that both have given us good results. Many experienced growers prefer a two-part nutrient for hydroponics and also for coco, but for soil most commonly a one-part nutrient is used. We would recommend a one-part nutrient to a novice grower wishing to try hydroponics and after several attempts of growing with a one part, maybe try a two part to see if your results improve. The main thing is the nutrients that you buy are of a high quality a good one or two-part nutrient can both deliver amazing results if used correctly.

How do I know if I underfed, and what do I do?

If plants are lacking the nutrients they require they will kick into action themselves and take the nutrients from their bottom leaves and deliver it into the top new growth that is developing, this will turn the bottom leaves a pale yellow, a sure sign that your plants are underfed. Raise the amount of nutrients you have been applying just slightly (don't overdo it) over a period of a few days and watch for signs of the yellowing to stop, this should solve the problem of under feeding your plants.

How do I know if I overfed and what do I do?

Probably the first signs you will see that you have overfed your plants will be some curling of the leaves and deformed new growth that is twisted and curled, very dark green in colour. Immediately you need to flush your plants with just plain water or you can use a flushing solution in the water if the plants are really bad. When refilling your hydroponic system or watering your soil or coco make sure to only start with a half strength nutrient solution for a few days until you can see that the new growth is looking normal again.

Why use additives?

Additives and boosts can be added to the water with your nutrients, and can assist plants in many ways. There are many additives and boosts available and most commonly they are designed to help a plant produce quicker growth and more yield from your fruits or flowers. There are also additives designed to assist plants internally and strengthen plant cells, helping to fight against attacks from pests or diseases. Using an additive or boost is definitely worthwhile if you wish to gain the maximum yield from your indoor garden.

When do I mix my nutrients and additives into the water?

It is best to leave tap water for at least 12 - 24 hours for the chlorine to dissipate from the water and for the temperature to reach the desired level, and then your nutrients and additives can be mixed into the water ready to fill your hydroponic system. If using an organic hydro nutrient we recommend mixing it into a jug of warm water before pouring into your main tank, and also definitely use an air pump and stone to keep your nutrient solution mixed well and highly oxygenated.

How often do I change my nutrient solution?

We advise our customers to change their nutrient solution weekly in re-circulating hydroponic systems, but if you have to leave it longer a couple of weeks will be ok. Keeping water fresh for plants is essential, you wouldn't want your food or water supply to be old.

What is the ideal temperature for my nutrient solution?

A temperature range of 21 - 24 degrees is adequate, if you have problems with reaching this temperature you will need a nutrient solution heater to help raise and maintain the required temperature.

Should I use an air pump and stone in my nutrient tank?

Yes, it will help to keep your nutrient solution mixed well and also raise the levels of oxygen in the water, this will help benefit your plants.


What type of light do I need for seeds or cuttings?

Fluorescent lighting is the best to use for propagating and raising seedlings or cuttings. HID lighting can be used with a Metal Halide lamp (blue spectrum) at a distance, but HID lighting is a lot more expensive to run than fluorescent lighting. Compact fluorescent lamps are available in 125w and 250w sizes and reflectors to hold them, also propagation lights with 55w lamps can be used, but the most popular choice of lighting unit now used for propagation is the Lightwave T5 fluorescent units. These units have become a huge hit for raising seedlings or cuttings and also they are a most efficient light unit for their size.

Do I need a propagator for seeds or cuttings?

Yes, a propagator is needed especially for rooting plant cuttings under a light. Seeds can be removed from a propagator as soon as they have sprouted in their germination plug and put under a light to begin their vegetative period, but cuttings will require a little longer in a propagator than seeds as the roots will take longer to develop and this requires a high humid environment provided by the propagator.

What humidity levels do I need for propagation?

For propagation it is best to aim for a humidity level between 85 - 95%. If a good quality propagator is used this should help to maintain the correct levels inside it easily, a light mist of water inside the lid of the propagator will soon raise the level if needed.

What temperatures are required?

Keeping a temperature of around 21 - 25 degrees is best for your young plants.

How long do I run my lights for propagation?

Your lights should be on for a minimum of 18 hours, some growers choose to run their lights for 24 hours, as this is also fine.


What size light will I need?

The size of the light you will require depends on the floor space you are going to be using. You can however use a higher wattage light for your growroom as long as your ventilation can remove the excess heat produced from the lamp. We recommend a 250w HID light for an area of about 80 x 80cm, a 400w HID light for an area of about 100 x 100cm and a 600w HID light for an area of about 120 x 120cm. Smaller and more confined spaces can be lit with compact fluorescent lamps as they emit very little heat.

What color light do I use to grow plants?

Plants respond well to a blue spectrum light for their growing period. If using HID lights a metal halide lamp will be needed, these emit a blue light and can be run with your HID ballast. Compact fluorescent lamps in blue can also be used for smaller rooms to grow plants.

What color light do I need to flower plants?

Plants that are required to produce flowers or fruits are finished under a red spectrum light. When the amount of light hours received by your plants is reduced to switch them and initiate flowering, a red spectrum lamp should be used. High Pressure Sodium lamps are used for HID lights and deliver plenty of red lights for your flowers to develop. Compact fluorescent lamps are also available with a red spectrum, great for flowering plants in very small spaces.

Is it possible to provide too much light?

No, as long as your growroom ventilation can cope with the heat from the lamps it is ok to provide additional lighting, especially when flowering and fruiting plants to gain extra yield.

What distance do I keep my reflector from my plants?

There are many recommendations given for the distance between your lights and your plant canopy, the simplest way to determine the distance between your light and your plant canopy is to hang your light above your plants and turn it on, after several minutes of it running place your hand halfway in between the light and plants for about 30 seconds and if the back of your hand is not affected by any heat you can lower the light slightly and try again with your hand until you find a distance that just slightly warms the back of your hand. This should give you an acceptable position that will not affect the tops of your plants with any heat stress.

What's a better reflector to use: open end or closed end?

We prefer to use a closed end reflector, as this design will deliver all light produced from your lamp downwards towards your plant canopy. The only downside to using closed end reflectors is they can build up heat below them considerably from the lamp, so as long as your ventilation is adequate in removing the heat produced from these reflectors then we recommend you use them. A Diamond or Supernova reflector is a great example of a closed end reflector. For growrooms where heat can be an issue we recommend you use an open-end reflector to allow any heat from lamps to escape quickly and be removed.

How often do I need to change my lamps?

Most growers tend to change their HPS lamps every 9 - 12 months if used regularly for 12 hour periods. If using MH lamps for 18 - 24 hour periods we recommend a maximum of 9 months use before changing them.

Can I use any size lamp with my ballast?

No, unfortunately you can't. Nowadays ballasts are built to run a specific size lamp and will not be suitable to use with any lamp other than that the size recommended. There are dimmable digital ballasts now available that can run at different outputs, most commonly they have a 400w setting, 600w setting and also a boost setting, allowing a 400w or 600w lamp to be used.

Why must I have a contractor/relay for my HID light?

A contactor/relay is used to control the electrical loads used to ignite and run High Intensity Discharge (HID) lights. Most contactor units will have two plugs that need connecting to a mains power supply, a box containing a relay, and sockets to plug your HID lights into. One of the contactor plugs is plugged directly into the mains power supply, and the other plug is plugged into a mechanical or digital timer and then into the mains power supply. The timer will control the on and off periods for the lights and the contactor will safely control the load that passes through to the ballast and lamp, allowing frequent On/Off cycles without lamp failure.

What is air cooled lighting?

Air-cooled lighting reflectors are designed to be fitted inline into your ventilation to remove the heat from your growroom and also from your lamp. Air cooled reflectors are built with a spigot attached at either end or a cylinder design that can easily be connected into your ducting and glass is used to seal the reflector to allow the heat to be removed but stop any odours entering the reflector and your extraction system. Air-cooled reflectors are a great choice for growers who are going to be using a confined small area that can suffer with heat problems.


Do I need ventilation in my growroom?

Yes, plants will need a regular supply of fresh air rich in Co2, and any hot stale air will need to be removed from your growroom.

Do I need a fan for my air inlet and outlet?

A small growroom that has only one light used can sometimes require only one fan for the extraction system and fresh air can be pulled into the room passively through inlet holes placed at the bottom of the growroom with the extraction fitted at the top. Growrooms that are large in size and use more than one lamp will certainly require a fan for the inlet and also the outlet, try to match the flow of air coming into the growroom equal to the flow of air being extracted from the growroom to provide negative air pressure inside the room..

What size extraction package and inlet fan should I purchase for my grow room?

In ventilation air movement is measured in cubic metres (m3), so to find out the size of extraction kit and inlet fan required for your growroom you will first need to calculate the cubic metres of air that is in your room. This is simply done by measuring the length, width and height of your room in metres. Then multiply the three figures to give you the total size of cubic metres of air in your room. Then you can multiply the total figure by the ACH (air changes per hour). For a growroom with one HID light being used the air in the room should be extracted and replaced at least 20 times per hour. An ACH (air changes per hour) of 20 would mean the air is exchanged every three minutes.

For a growroom with more than one HID light being used the air in the room should be extracted and replaced at least 30 times per hour. An ACH (air changes per hour) of 30 would mean the air is exchanged every two minutes.

Example: A growroom that measures 2m x 2m wide x 2.5m tall = 10m3, this figure now needs to be multiplied by the ACH.

One light - 10m3 x 20 ACH = 200m3

Two lights or more - 10m3 x 30 ACH = 300m3

It is always better to exceed the total amount of air to move by at least 10%, as this will help to compensate towards the heat from the lamps and keep your temperatures under control.

Do I need my extraction kit and inlet fan to operate all the time?

No, the main time for the ventilation system to be running is when your grow lights are on. If temperatures rise too high whilst your lights are off you can set the extraction to turn on several times in the dark period to help lower the temperature inside. If odours are a problem from your garden then you can run the extraction permanently, just watch the temperatures don't become too low inside the room.

How do I control my fans to keep the required temperatures?

The best way to control both the inlet and outlet fans to keep the required temperature is with a unit that has a fan speed controller with thermostat built in. We stock the Primair fan speed controller unit with thermostat, this requires only one plug to a mains supply and it can have two small or large fans connected. The thermostat dial can be set to the required temperature and both fans have an idle speed, which controls the speed of the fan when the temperatures are reached. Basically if you set the temperature to 22 degrees Celsius the fans will turn on to full speed if this temperature is exceeded and if the idle speeds are set at 0, the fans will shut down completely when the target temperature is reached. If the idle speeds are set at 50% then the fans will continue to run at 50% RPM when the target temperature is reached. This unit allows total control for room temperatures at the turn of a dial and can help to prevent dramatic temperature fluctuations in your growroom.

What is better to use, aluminium or acoustic insulated ducting?

Acoustic insulated ducting is better to use than aluminium ducting as it helps to greatly reduce the noise levels created by the fans and the air travelling through the ducting, with its acoustic properties.

Do I need to use a fan inside my grow room?

Yes, the movement and circulation of air inside your growroom is also very important. Using an oscillating fan or a wall and floor fan can be very beneficial and will help to replace the air around the plants more easily. The creation of a slight wind inside your growroom will also help to strengthen plant stems, and when flowering or fruiting plants it can help to prevent botrytis (bud rot) from forming. Hot humid conditions with little air movement are a great place for bud rot to thrive.

How do I know what my room temperatures and Humidity levels are?

To keep a track of your growroom temperatures you will need a thermometer and also a hygrometer that displays the levels in your growroom. We sell a digital growroom thermometer and hygrometer all in one unit that displays both readings on a large screen and also records the minimum and maximum levels reached. Using a temp dial allows an accurate and easy way to see your levels without any guessing.

What humidity levels do I need in my grow room?

When propagating seeds or cuttings a humidity level of around 85-95% is required, this can easily be achieved with the use of a propagator. When plants are in the growth stage a humidity level of around 65-75% is required, and when flowering or fruiting plants a humidity level of around 45-55% is required.

What temperatures do I need in my grow room?

For different plant varieties temperatures can differ, but most commonly the temperature should be between 21-25 degrees Celsius when your grow lights are on and it is the day period for the plants, and for the night period the temperature should drop slightly to about 18-21 degrees Celsius. Too big of a fluctuation with temperatures can result with plants suffering and slow growth. Try to keep a constant regular temperature and your plants will love it.

When my fans shut down cold air comes into my grow room through my ducting - what do I do?

This can be a common problem and can easily be solved with the use of a back draft shutter. Back draft shutters are circular with internal hinged doors and can be easily installed into your ducting to prevent any air movement when your fans are off. When your fans turn on the pull of air will easily open the hinged doors to allow the air to travel through, when your fans turn off the hinged doors will close stopping any air passing in or out of the fitting and keeping your growroom temperatures at a more constant level.

How do I keep pests from entering via my fresh air supply ducting?

There are filter chambers available that can be fitted into your ducting to prevent anything entering your growroom, or for a cheaper option you can use a pair of stockings to cover the end of the ducting. This will allow air to travel freely but will stop any pests entering, and they can be changed regularly at a very low cost.

I have a huge place but don't need a big carbon filter hanging from my ceiling?

You don't have to you can have two smaller carbon filters suspended and connected together to the main extraction fan instead of one big heavy filter. This allows for one hole to still be used for expelling the air from your growroom. The fan can be situated near to the main outlet hole and connected with ducting. The other side of the fan facing the growroom can have a Y or T section to split the ducting into two sections, and the ducting can have damper units fitted to control the flow of air allowed to travel through each line of duct, as air follows the path of least resistance. The damper units can be closed or opened to balance the flow. At the end of each run of duct you can reduce down to suit the smaller carbon filters. This spreads the weight across your ceiling and can also improve your extraction, as it removes hot stale air from two points in your growroom.


What is PH?

PH (potential hydrogen) is a method for measuring your water to test and determine how acidic or alkaline it is. PH is measured on a scale of 0 - 14 with 7.0 being neutral, any reading above 7.0 is alkaline and anything below 7.0 is acidic.

How do I check my PH value, and how often?

The easiest and most accurate way to test your PH value in your nutrient solution is with a PH meter, there are also manual PH test kits available but these are not as accurate.

How often do I balance my PH value?

Your PH value should be monitored regularly (every 2-3 days) in a hydroponic growing system and adjusted to suit to the value you require.

Why is it important to maintain the PH level in my nutrient option?

Too high a Ph value or too low a PH value will result in a nutrient lockout as plant roots will not be able to correctly absorb the nutrients supplied, resulting in poor slow growth.

What is EC?

EC (electrical conductivity) is a method of measuring how strong your nutrients are in your water. When nutrients are applied to the water the salts allow an electrical current to pass through the water and this current can be measured with an EC meter to give an accurate reading of how strong your solution is.

How do I check my EC value, and how often?

An EC meter is recommended for this job, simply place the end of the meter with the probe into the water to display your EC value of your nutrient solution.

How do I adjust my EC value?

To raise the EC value in your nutrient solution, simply add more nutrients to your water. To lower the EC value in your nutrient solution, simply add more water and adjust your PH value to suit.

Why is it important to maintain the EC level in my solution?

Plants grown hydroponically depend on a regular supply of nutrients to assist them in their struggle to grow. Keeping a good level amount of nutrients in your supply tank means plants have access to air, water and nutrients at all times.

How often should I clean and calibrate my PH & EC meters?

Cleaning your probes on your meters is very important, if the probes on your meters are dirty or contaminated it can affect the accuracy of your reading. They should be cleaned and maintained at least every two weeks and calibrated to ensure accurate readings are provided. Do not store your EC meter in any solution, but your PH meter should be placed into a storage solution whilst not in use.

Pests & Plant Health

Is it actually important to keep my grow room clean?

Yes, a clean growroom is a healthy growroom. Keeping all debris of the floor and out of the room will prevent insects and fungi breeding in hidden areas. Your tools clean and sanitised and always make sure you are clean and pest free when entering your growroom. This should help to prevent any unwanted visitors or diseases.

How can I identify pests in my grow room?

Sticky Fly Traps are the easiest things to use to catch insects in your growroom, they can be placed up high for flying insects and down low for crawling insects. Once caught the best thing to use for identifying the pest if not clearly visible is a microscope, this can display the insect easily for you to view and identify the little critter.

How can I treat pests in my grow room?

Once you have identified the insects that have inhabited your growroom and plants you can purchase a product to eradicate them. Most commonly pest control products are available in a spray form to make covering the plants and insects easy. There are also Bug bomb smoke generators that can be used to eliminate a wide variety of pests, these require lighting and then they pour out the Permithrin smoke into your room, when lighting close your growroom door behind you quickly with your ventilation shutdown. Also products to treat water and media of any unwanted visitors are also available, we stock them all.

My plant leaves are curling upwards?

When plant leaves are curling upwards it is normally a sign that they are struggling to retain moisture. It could be that your grow light is too close to your plants and will need raising slightly or a fan in your room is blowing too heavily directly onto your plants. Try to control the temperatures better in your growroom environment.

My plant leaves are curling downwards?

When your plant leaves are curling downwards it is normally a sign to indicate that the nutrients being applied to the plant roots is way too high. To correct the situation flush your plant media with just water for a few days and then go back to half strength nutrient solution until growth picks back up and looks normal.

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