Nitrates and Ammonia

These compounds are relatively a lot less toxic than nitrates and ammonia. At levels 50mg/litre they begin affect fish, especially fry. They retard growth and particularly affect the development of fins. Coloration begins to be affected and there is more susceptibility to disease. Koi are less affected and have been known to tolerate levels of up to 500mg/litre.

EFFECTS. Any levels of nitrates above 12.5mg/litre tend to promote the growth of algae. The nitrate concentration can, however, get worse in a pond with an efficient filter with few or no plants. It is further exacerbated by the use of a U/V sterilizer, overcrowding with fish and over feeding. This is because the filter is effectively killing the algae that would be utilising the nitrates and in the course of processing filtered material from ammonia through to nitrites, it ends up feeding even more nitrates back into the pool.

With even low levels of nitrates encouraging the growth of algae, the susceptibility to the scourge of blanket weed is by far the worst problem. Also with the higher levels of nitrates, the threat of the blue-green algae species loom and with these can come toxins that spell the death of all life in the pond.

EMERGENCY TREATMENT. 1.Partial water change.

2. Remove excessive detritus from the filter.

CURES 1. Encourage healthy plant growth in the pond. Oxygenating weeds are the most effective.

2. If this is not possible then adding an anaerobic stage to your filter system is necessary. Here denitrifying bacteria can break down the nitrates to nitrogen and oxygen. I have never had much success at this and find it easier to work with plants.

Even if necessity forces you to do it outside the pool, you can employ the missing link in the nitrogen cycle, to work in your favour. Use plants, particularly fast growing ones e.g. watercress, growing in the filtration media to use up the nitrates in the water as it passes through.

Recent developments in sophisticated filters, particularly those from the likes of Nexus have proved that the break up of ammonia compounds can be achieved right down to nitrogen in one filtration chamber. The claim is based on the huge surface area of the filtration medium on which the bacteria grow. The industry waits with baited breath for further developments.

3. Ensure the pond is never overstocked with fish.

4. Do not over feed the fish especially when the temperature of the water drops below 8c.

5. Does the pond need a clean out?