Kill the “algae”

If you can kill the algae faster than it is growing even if there are high nutrient levels in the water or if you can remove the nutrient source then the water must remain clear because the algae population cannot build up to levels which cloud the water. Under normal conditions it is difficult to remove the nitrates and as such there is always food on which the algae thrive. Plants to some extent help in removing nitrates but never reduce the nitrate to zero levels otherwise the plants would die.

The UV light has one single function. It is designed to kill algae. The action of an UV light is to kill the algae faster than it forms … it does not eradicate algae! This is an important point to understand. Suspended algae in water, is pumped through the UV unit. The living algae is irradiated and killed. If there is enough power in the UV unit to completely suppress algae growth then the water will remain clear. If the power or irradiating effect of the UV is insufficient then water will remain cloudy.

If a UV unit is not clearing the pond water then there are 3 possible reasons.

1.) The lamp has gone beyond its active period (max 8000 hours or approx 1 year running 24/7) after which it must be changed. After a period in use the capacity to irradiate is completely lost. Lamps do not always last 8000 hours.

2.)  UV may not have enough power ( Watts ) for your specific situation. You have very warm water and your pond is probably overstocked with fish. Remember also your fish have grown over the last year and thus produce more nitrate nutrients. This might mean that what worked last year will no longer be sufficient. However without knowing dimensions of your pond or volume and your existing UV wattage I cannot really comment. Suffice to say UV works every time if correctly sized and maintained for prevailing conditions. Send me this information and I can comment further.

3.) If your UV contains a quartz tube (and most do) there is a possibility that it is “fogged up” thereby reducing light transmission. In this case it needs cleaning since this also results in reduced irradiation levels. Irradiation capacity is expressed as Watts … thus an UV is specified as 8 watts, 15 Watts and so on.If I have to guess I would say your UV is undersized for the prevailing pond conditions.

It is true to say that most UV claims are overstated since the specification is provided for a low fish stock in ponds of lower temperature and in a partial shade situation. These conditions rarely exist in climates like yours. In practice this means if you see a specification based upon your pond volume then by virtue of your location/climate you probably need double that specified wattage.

Don’t feed the alga

All living creatures need nutrients (food) to grow. Deprive the organism of nutrients and the organism dies. Certain types of bacteria in an anaerobic environment consume nitrates and produce nitrogen gas in the process. The nitrogen gas escapes from the water surface and the nitrate levels drop.

By introducing these bacteria and providing areas where anaerobic conditions exist (as is the case in boundary surface layers in all ponds and all biofilters) the nitrate levels will ultimately be reduced to zero. Under this condition algae cannot survive for any length of time and water remains clear.