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The Hydroponics Manual: The Nutrient Solution

Modern nutrient solutions come in several different types. It is important to make sure that the solution you use is the best for your purpose. Solutions that are designed specifically for soil, often called plant "foods" or fertilizers, are suitable only for soil and not for hydroponics. One of the reasons for this is that various trace elements can be relied upon to exist in soil and they are not usually added to the solution. The other reason is that much cheaper and less soluble materials can be used with soil nutrients. They are also often crudely formulated and contain the wrong form of crucial elements such as nitrogen.

True hydroponic nutrient solutions on the other hand must be complete, containing every element needed for plant growth in its most soluble form. This is why hydroponic solutions tend to be more expensive. Do not be put off by this as the total cost of nutrients is still a very small part of your overall expenditure and saving money on nutrients is to run the risk of serious problems. Always use the best quality nutrient solutions as the solution is the only source of nutrition in hydroponics so it must be of the highest quality. The advantage of course is that every time you water your hydroponic plant, you can be sure that it has a full profile of nutrients in exactly the right proportions. You can never be sure of this with plants in soil. In fact, it is almost impossible to maintain a good balance of nutrient with soil in containers.

While it is true that plant "foods" for soil are not suitable for hydroponics, it is quite possible to use hydroponic solutions for soil growing. You can actually achieve great improvements this way because the plant is fully supplied as it may not have been before. There is a risk, however, that you may overfeed the plant so we recommend that you make the solution at only half the regular strength and that you only use it once a week with soil. The symptoms of over feeding are easy to spot and quick to remedy, see Trouble Shooting, below.


Single Packs

The reason that liquid nutrients are usually supplied as twin packs is that some of the components are incompatible in concentrate and will cause precipitation when they come together. Once they are diluted into a "working solution" however, there is no problem. There are several good single pack liquid nutrients on the market now, including Formulex. In Formulex, the antagonistic elements are held in a chemical complex to avoid precipitation. It is an ingenious solution to the problem of precipitation and is highly suitable for growing house plants and for all soil gardening.

Twin / Triple Packs

(shelves of nutient products in the Esoteric Hydroponics shop)
Selection of Nutients

There is no question that for serious hydroponics there is still no better product than a good quality liquid twin or triple pack nutrient solution. Twin and triple packs are very easy to make up and use and they are usually provided with comprehensive instructions to ensure success.

Optimum and Power Gro are well established twin pack nutrients. Optimum and Power Gro have been on the market for over ten years but their formulations have been continually modified and improved in the light of new information and more experience. Ionic and GH Flora Range Triple Pack nutrients provide an unbeatable comprehensive diet of primary and secondary nutrients plus unique pH buffers to keep nutrients fully available to the plants.

Optimum, Power Gro, Ionic and G.H Flora Range are now available right across the UK so for supplies or more information, contact Esoteric Hydroponics.

Applications for Nutrients

Soil Growing

Plants growing in soil can be fertilised with any of the plant "foods" on the market. Follow the directions on the packet but do not overdo it. If you feed too often or with too strong a solution, you can cause overfeeding. The soil will hold the excess fertilizer salts and this will tend to build up with each application. Avoid this by watering with plain water several times between each "feed".

If you wish to use a hydroponic solution with soil, we would suggest a single pack solution such as Formulex. This is a full featured solution but is slightly less concentrated than the twin or triple packs. It is pH stabilised and will produce great results with soil.

It is also possible to use twin or triple packs with soil. The important thing to remember, whichever solution you use is not to overfeed. Nutrient solutions should always be applied to soil at half strength and no more than once a week. Watch out for the symptoms of overfeeding which are very easy to see. The leaves will have a tendancy to curl downwards and become dark green, brittle and glossy. If this happens, flush the soil by watering heavily with tap water. Wait a week or two before resuming the feeding routine.

Passive Hydroponics (Pot Culture)

Pot culture is the simplest form of hydroponics and involves the use of an inert medium such as perlite or greenmix in a plastic pot in place of soil. Despite the ease of using this system, do not make the mistake of under-estimating it. Incredible results have been achieved with flowering plants and vegetables and it is an ideal first step away from all the problems of soil.

If you are using pot culture for foliage plants only, you will be well suited with a single pack nutrient solution such as Formulex. However, if you wish to grow flowers or vegetables, you should consider using a twin or triple pack nutrient solution such as Optimum, Power Gro, Ionic or GH Flora range.

Recirculating Systems (other than rockwool)

These systems include NFT (Nutrient Film Technique) and Flood and Drain tables. It is normal with these types of systems to monitor the nutrient solution and to top it up regularly in order to maintain the right conductivity or "strength".

For this kind of hydroponic system, you should always use a top quality twin or triple pack liquid nutrient.


This is a distinctly different medium and requires a specialised nutrient solution to get the best results. There are very few nutrient products on the market designed specifically for rockwool but if you can find one you should use it. Most nutrient solution are formulated for rockwool. These nutrients are now available from Esoteric Hydroponics.

Q: Is hydroponic produce as healthy and nutritious as soil grown food?
A: Yes, every bit so. Hydroponic nutrient solutions are blended from mineral salts and are formulated to contain all the mineral elements needed for plant growth. Green plants can only take up elements which are exactly the same whether they come from manure or from a nutrient solution. Recent research has confirmed that the food value of hydroponic produce is at least as high as the soil grown alternatively and in many cases it is superior.

Making up nutrient solutions

Making up nutrient solutions is very easy. First of all you need a container to make it up in. It is always best to make up as large a quantity as possible. Nutrient products come supplied with very detailed instructions to make life easy.

A 200 litre drum is an ideal size for a mixing tank and 200 litre drums are very commonly available. It is quite possible, however, to make up just a bucket or watering can full, remembering that the mixing ratio is 3.5mls of A & B (& C) per litre. The measuring flask enclosed with the pack makes it easy. Any plastic container will do as a nutrient container but remember to keep it covered when storing nutrient solution. If light is allowed to get to it there will eventually be algal growth in the tank which you will recognise as a green slime, unsightly but not harmful.

You will need to know the volume of your container. Large rubbish bins for instance are usually about 70 litres. If you are using your nutrient solution for pot culture in which it is supplied to the plant from a large tank or drum, you can quickly standardise your mixing procedure.

When you make up your first drum, you will need to follow the manufacturer’s directions very carefully. You will however, need to add a small amount of pH Up or Down to correct your pH. When you do this keep a careful record of the amount you add, it may only be a few drops. Once you know how much is needed, it will be a simple matter in future to add it to the water in the drum before you add the nutrient. If you do this you can normally be sure that your final pH will be correct.

TIP: the pH of town water supplies can fluctuate during the year so you should always make a final check of pH after making up a large batch of nutrient solution. A good quality product, such as the nutrients mentioned will be found to contain comprehensive instructions to make all this very easy. Once you have established a routine, you will find it a breeze.

Q: Why do good quality twin-pack nutrients come in Grow and Bloom options?
Q: Why do good quality triple-pack nutrients come in Grow, Bloom and Boost options?
A: Optimum and Power Gro are both available in two distinct formulations, each with a different ratio of the macro elements. The Grow formulation is designed to supply the needs of the plant during the vegetative stage of its growth cycle. High levels of nitrate-Nitrogen will encourage rapid leaf and shoot growth and maximise the potential of the young plant to produce fruit and flowers later in its life. The bloom formulations are dedicated to the fruiting and flowering stage of plant growth, containing reduced levels of nitrogen but greatly enhanced levels of phosphorous and potassium, the elements required for development of buds and flowers. The change over from grow to bloom is especially recommended for strawberries, tomatoes and flowering plants. Ionic and GH Flora include the above with an extra Boost formulation to enhance the Grow and Bloom nutrients.

Composition of the Nutrient Solution

A modern solution is formulated from a large number of mineral salts. These are chosen for their purity in the first place because they are calculated to the nearest part per million (ppm) in the solution. It is not possible to formulate accurately with impure or contaminated materials. The second requirement is solubility. All components of a hydroponic solution must go easily into solution, leaving no residue or precipitation. One of the ways of assessing the quality of a product is to examine the bottom of the tank. Any serious sedimentation after use would possibly suggest the use of cheap and unsuitable materials in the formulation.

Trace Elements

A good nutrient solution should contain a full profile of trace elements, usually known as micro-nutrients in hydroponics. The essential micro-nutrients are iron, manganese, copper, zinc, boron and molybdenum. Some solutions may contain other less common elements such as nickel but those are the key ones and no true nutrient solution would be without them.

The best solutions will supply most of their trace elements in the form of chelates which is the usual choice of professional growers. A chelate (pronounced keylate) is a form of the element in which the molecule is locked up in a kind of organic jacket which ensures its stability within the solution. Once the molecule has been taken up by the plant, it immediately becomes available to the biological process. This is particularly important in hydroponics because the pH of the nutrient solution can fluctuate quite a lot and ordinary trace elements will easily precipitate and become unavailable if the pH is not to their liking, even if it is only for a short time. This is particularly important with the key trace element iron which is highly unstable in its non-chelated form. Chelates are many times more expensive than the simpler forms of the element. This is a very good indicator of the quality of any nutrient solution if it contains fully chelated micro-nutrients. Boron and molybdenum are not usually chelated as they are very stable in other forms.

PH and Conductivity

PH and Conductivity are the two most important variables in nutrient solution management. A basic understanding of them is essential for successful hydroponic gardening.


PH is a measurement of the acidity or alkalinity of a solution. On a scale of 1-14 neutrality is represented as 7. The ideal pH for almost all hydroponic applications is 6. PH for rockwool cultivation should be slightly lower, ideally about 5.8.

Different Plant Species

Plants growing in soil have widely differing preferences for pH. This is not the case in hydroponics and all plants in hydroponic systems will function best at a nutrient pH of 6.

Measuring pH

This is best done with a meter but there are also various kits available which use liquids and papers. Kits are adequate for applications such as pot culture where the nutrient is supplied to the plant once and is used up before being replenished. Growers using re-circulating systems such as NFT or Ebb and Flow will certainly need a meter to monitor their solution accurately. Meters will require regular calibration and instructions for this are supplied with them.

PH in Passive Hydroponics

Passive hydroponics refers to growing in pots full of a medium such as perlite or greenmix or to hand watering rockwool slabs.

Normally, for this type of cultivation, it is recommended that the grower make up a large container of nutrient at a time. A 200 litre plastic drum is an ideal container. Once this is made up to the correct strength (conductivity), the pH can be checked and adjusted to the ideal level of 6. A careful note should be made of the exact amount of pH Up or Down that is added at this time. A good pH can be used for this because although the pH measurement takes longer than with a meter, it only needs doing occasionally in passive systems. The nutrient solution in the drum should remain quite pH stable and can be applied to the plants as needed.

PH in Active Systems

Active systems are ones in which the nutrient solution is supplied to the plants by pumping, such as Ebb and Flow tables or NFT systems. In most domestic systems, the solution is re-circulated to the roots continuously over a period of time.

In an active system, the pH will need checking and adjusting in the main tank on a regular basis. In most systems, fresh water is added to the tank to replace that used by the plants. The incoming water is usually of a higher pH than the nutrient solution so there tends to be an upward drift in pH. This can be corrected by the regular addition of small amounts of pH Down. This process of pH control can be carried out with a pH kit but as it needs doing often, the busy grower will be better off using a meter. If the water supply is classified as hard, the grower must be very careful with re-circulating systems. (See note on hard water.)

Hard Water

Hard water is characterised by high levels of bicarbonates and it makes itself known by depositing lime scale in kettles and by reducing the lathering capacity of soap. Hard water will usually have a high pH but this is not always necessarily the case. What will distinguish hard water is that it will take much more acid to reduce the pH than with an equivalent sample of softer water. This is because the bicarbonates have to be neutralised and this uses up quite a lot of acid.

The obvious problem for the grower is the addition of quite large amounts of acid on a regular basis. If the grower is using phosphoric acid this may lead to a build up of phosphate in the nutrient tank over time. High levels of phosphate in the solution can inhibit the uptake of other salts, like zinc, and cause general nutrient imbalance.

Solutions to Hard Water Problems

The first and most obvious solution is to change the nutrient tank regularly. This will reduce the chances of phosphate accumulation and ensure maintenance of a good nutrient profile. Frequency of changes will depend on tank size and number of plants. In very hard water areas, however, a large amount of phosphoric acid will be needed to correct pH when nutrient is first made up.

It is possible to used nitric acid to control pH. This will overcome the problem of phosphate accumulation but nitric acid is a very unpleasant and dangerous liquid. It should never be handled by anyone who is not experienced with aggressive liquids and all good laboratory procedures should be observed. Nitric acid will only solve the phosphate problem, it will not make any difference to the high levels of calcium and other minerals which will eventually accumulate in the tank.

The best solution by far is to use a specific formulation which is usually based on more acidic components. Hard water nutrients were formulated in response to demand from growers in various areas of the United Kingdom such as London, Thames Valley and other areas with very hard water. It was specifically formulated to correct the pH of alkaline water and minimise the amounts of phosphoric acid that are required to maintain it at correct levels. It also takes account of the other minerals to be found in hard water and use of this product will ensure the best possible results in hard water areas.

Another solution would be a reverse osmosis filter (RO unit) which will remove the mineral ions by passing water through a very fine membrane. The water produced can be very pure and will allow normal nutrients to be used with complete confidence.


The conductivity of a solution is an expression of the capacity of that solution to conduct an electric current. Distilled or de-ionised water will conduct virtually no electricity at all and will therefore have a conductivity reading of zero. As salts are dissolved in the water so the conductivity of the solution increases. The conductivity of a nutrient solution is therefore a measurement of its strength as indicated by the actual amount of salts dissolved.

Conductivity is usually expressed in terms of CF. CF stands for Conductivity Factor and the units of measurement are usually milliSiemens, microSiemens or Siemens. The difference between these is purely in the placing of the decimal point. There are a thousand microSiemens in a milliSiemen. A CF unit is equal to a hundred microSiemens so there are 10 CF units to a milliSiemen.

CF Meters

CF meters usually read in milliSiemens or CF units but for the grower it is simply a matter of getting the decimal point in the right place. As a rule of thumb, it can be said that a good conductivity level for most purposes would be 2.0 milliSiemens (expressed as 2.0 mS/cm2). We can call this a standard working solution. Therefore: standard working solution = 2.0mS = 2,000mS = 20 CF units


Conductivity is sometimes expressed as EC (Electrical Conductivity). Units of EC are now identical to CF units.

Parts per Million

Conductivity is sometimes expressed in terms of parts per million (ppm). One gram of any salt, dissolved in a litre of water will make a solution containing 1000 ppm of that salt. However, different salts have a different capacity to conduct electricity so two solutions made with different salts could both be 1000 ppm, but have quite different readings on a CF meter. It is therefore not possible to make an exact conversion from parts per million to CF units, however as most nutrients solutions have approximately the same ration of constituent salts we can make an approximate conversion.

1mS = 10 CF units @ 640 ppm


Standard working solution = 20 mS = 20 CF @ 1280 ppm

Meters for pH and Conductivity

Many different meters are available from Esoteric Hydroponics. There are cheap digital meters such as Eutech and we also stock the amazing Conductivity Truncheon and pH Wand from New Zealand which use flashing LEDs to show the CF or pH reading. These are accurate and reliable and cannot be too highly recommended. They also carry a full two year warranty which is quite remarkable for such sensitive instruments. Esoteric Hydroponics also stock Buffers and Standards. PH buffers are liquids of a known pH, usually 7, which can easily be used to check and correct the accuracy of your pH meter. CF Standards are solutions of a known conductivity which are used to calibrate your conductivity meter.

PH and Conductivity in Rockwool Systems

Plants grown in rockwool slabs need slightly different nutrient regimes than in other systems. PH should be somewhat lower, at 5.8 rather than 6. Conductivity should also be slightly lower than in other applications. It is very important to remember that the readings in the tank may not reflect the reality within the slab. Nutrient should be extracted from the slab regularly for measurement. In a well maintained system there should not be too much variation between tank readings and those obtained from within slabs. If conductivity begins to rise in the slab it will be an indication that irrigation is either too infrequent or too short. It is necessary to trickle nutrient into slabs for just long enough to get a 10-15% run off. The timer should be adjusted to provide this amount of nutrient at least four times during the daylight period. More frequent irrigation may be beneficial. Remember that as plants grow they will take up much more nutrient and the watering cycle will need to be extended regularly throughout the life of the crop. The regular check of nutrient from within the slab itself is the most important routine for the rockwool grower. If the Conductivity begins to rise then the grower will increase irrigation to ensure run off at each watering cycle. If Conductivity begins to rise then the grower will increase irrigation to ensure run off at each watering cycle. If Conductivity remains high then it is a simple matter to flush the slabs.

Products for the Control of pH and Conductivity

PH Down

PH Down contains orthophosphoric acid (H3PO4). The concentration is 81% which is very strong so handle with care. Some products on the market are considerably weaker so check the concentration before you buy. This is a very dense liquid and should feel much heavier than water.


PH UP contains potassium hydroxide (KOH). This is a very caustic liquid and should be handled with extreme care. Always check the label before you buy for best value.

Health and Safety

PH control chemicals are highly toxic and aggressive liquids
Please follow these simple guidelines for safety and peace of mind.

  1. Always store these materials in a safe place, preferably in a locked cupboard. Always keep them out of reach of children.
  2. Always wear rubber gloves and protective goggles when handling any aggressive chemicals.

Nitric Acid

Many commercial growers use Nitric Acid (HNO3) for pH control. This would be a good option if you have hard water but it is not recommended for small scale growers. Nitric Acid is a very unpleasant and dangerous liquid, it is truly aggressive and should only be handled by experienced operators.

Never add water to Nitric Acid


There is a tendency amongst growers to suspect nutritional problems whenever their plants are not looking their best. In most cases the nutrients are not at fault and environmental problems are far more common. However, nutrient problems do of course occur at times and it is important to be able to recognise them. Assuming the grower is supplying the same solution to all his plants, we can ask the following questions to see if the problem relates to nutrition.

Q: Are all the plants (of the same species) affected in the same way?
A: If not and if for instance you have some plants showing problems while others look fine, then your problem is unlikely to be the nutrient. If you have a greenhouse full of tomatoes however, and they all show the same symptoms, then nutrient problems must be suspected.

If you have a problem that shows up in the foliage, usually as inter-veinal mottling or dead spots or as pale foliage or yellowing in the older growth or the new growth then you probably have a nutrient problem. The commercial grower will need to have an analysis of his main tank to find out what is happening but for the hobby grower the solution is very simple and involves a course of action that should be carried out whenever problems are suspected.

  1. Flush the plants. With pot culture this simply involves hosing lukewarm water through the medium until it is running freely through. This will remove any salt build up in the root zone. With re-circulating systems such as NFT or Rockwool, it will be easier to fill the tank with fresh water and allow it to circulate through the system to flush the root zone.
  2. Make up a fresh batch of solution, check and correct the pH and Conductivity. Restart the system as before. Keep a careful eye on the new growth which should be normal from that point onwards. It is a good part of routine to flush the root zone once every six weeks or two months as a precaution against salt build up.


All good nutrient products should include a full analysis of its components. It is very important for the grower to know what is being supplied to the plants so that adjustments can be made if necessary. If the product that you buy is supplied without an analysis, you should ask for one. You will normally find that manufacturers and suppliers will be glad to oblige.

Commercial Nutrients

Although commercial nutrients are formulated from the same materials as the best amateur ones, there is a major difference. For commercial growers there is the possibility to formulate specifically to the crop and also to take into account the grower’s water supply.

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