Hydroponics And pH

A basic understanding of pH 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. 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

pH scale

Measuring pH

This is best done with a meter but there are various kits using liquid and papers available. pH Test Kits are adequate for applications such as pot culture where the nutrient is supplied to the plant once and is set 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.

Bluelab pH Pen

pH In Passive Hydroponics

Passive hydroponics refers to growing in pots full of a medium such as Perlite, Pumice, Coco or to hand watering Rockwool Slabs. Normally for this type of cultivation we would recommend the grower to make up a large container of nutrient at a time. A 70l plastic rubbish bin or a 200l plastic drum make ideal containers. Once this is made up to the correct strength ( conductivity), the pH can be checked and adjusted to the ideal leved of 6.

A careful note should be made of the exact amount of pH UP or DOWN that is added at a time. In the future this amount can be added as routine when making up solutions and pH should remain pretty constant from batch to batch, although spot checks are recommended from time to time. A good pH Test Kit 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, NFT, Dutch Pot and Aeroponic. In most domestic systems the solution is re-circulated to the roots continuously over a period of time.

Hard Water

Hard water is characterized by high levels of Bicarbonates and it makes itself known by depositing lime scale in jugs and by reducing the lathering capacity of soap. Hard water will usually have a high pH, but not necessarily. 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 neutralized and this used up quite a lot of acid.

The obvious problem for the grower is that he will be adding quite large amounts of acid on a regular basis. If using Phosphoric acid this may lead to a build up of Phosphate in the nutrient tank over time. High levels of P in the solution can inhibit the uptake of other salts, Zinc for instance, 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 arias however a large amount of Phosphoric acid will be needed to correct pH when nutrient is first made up.
  • It is possible to use 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 mot 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.
  • Best Solution by far is to use a specific formulation which is usually based on more acidic components so as to correct the pH of alkaline water and minimize the amounts of Phosphoric Acid that are needed to maintain it at correct levels. It also takes account of the other minerals to be found in Hard water use of this product will ensure the best possible results in Hard water areas.
  • A reverse Osmosis Filter 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.

Soft Water

Soft water typically has a low pH due to the low amounts of calcium bicarbonates and other ‘light’ atoms and ions in the water. The most common method used for softening water is ion exchange, where the dissolved calcium and magnesium ions are exchanged for sodium or potassium ions. Sodium and potassium do not cause the problems that are associated with calcium and magnesium. The process is the basis for most water softening equipment on the market today.

Water enters a water softener where it comes in contact with a bed of tiny beads that hold sodium chloride or potassium chloride ions. Since the beads are chemically more attracted to calcium and magnesium ions, ion exchange occurs. The calcium and magnesium ions "stick" to the surface of the beads, dislodging the sodium or potassium. After the beads are completely exhausted, a system then regenerates and replaces the exhausted sodium or potassium in the field. After the extra solution is rinsed from the resin bed, the entire ion exchange cycle begins again.

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