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Clean Water Supplies for Hydroponics

The importance of clean water supplies for NFT, DFT and bag growing systems cannot be over emphasised. Water from ponds, dams and other surface catchments, and from shallow bores are quite likely to be contaminated by Pythium, Phytophthora or other disease organisms from time to time, although not always continuously. Roof water dams may be contaminated by dust borne fungal spores. Treatment of water supplies to prevent introduction of disease into hydroponic systems will thus often be essential and always desirable.

Roof water Dam and Greenhouse Treatment by ultra-violet or ozone sterilisation is not expensive to operate, but does require some capital investment. Which ever treatment method is used must be effective, but there are many ineffective installations.

We believe that continuous treatment of water in bulk tanks is probably the most effective method. This requires that raw water is held in a bulk tank and continuously circulated through a filter and UV filter, or is continuously injected with ozone, and that treated water for the hydroponic system cannot be drawn from the tank except through the filter.

UV treatment system
Certain precautions need to be observed with both systems if they are to be efficient. For UV filtration, the flow rate through the UV filter must not exceed the manufacturers recommended flow, and hence a throttle valve is fitted in the circuit to limit the flow to this rate. UV light is blocked in dirty water, and hence the water must be clear and passed through a 200 mesh filter element before treatment, and the treatment tubes within the filter must be kept clean. The output of UV lamps falls off with age and the UV lamps must be changed after the number of hours use recommended by the manufacturer (typically about 7,500 hours). UV treatment should precipitate any iron or manganese that is in the raw water.

Ozone treatment will precipitate organic matter, iron and manganese and some calcium from water containing them, and water should be filtered through a 200 mesh element before passing through the venturi or to the hydroponic system. The venturi sucks air into the ozone generator and injects bubbles of ozone rich air into the water stream. These bubbles must remain in contact with the water for long enough for the ozone and air to dissolve in the water. The water returning to the storage tank is injected through a diffuser pipe (a pipe drilled with many small holes) at the bottom of the tank. It is important that the water above the diffuser pipe is deep. If the tank is too shallow then water must be injected in a 3m or so tall wide pipe for maximum diffusion before discharge into the holding tank.

Ozone is toxic to humans and ozone in the air above the water in the storage tank is dangerous, and hence the tank must not be entered unless it is free from ozone.

Both of these systems will result in the stored water being treated several times during the night when there is little use of water by the hydroponic system, and during the day it is impossible for any water to be drawn by the hydroponics system that has not been treated at least once, and in most cases it will have been treated several times before use.