Is nitrate control really necessary?

Why are nitrate levels important?

Nitrate levels in aquariums need to be controlled as at high levels they compromise the health and well-being of the fish. This can eventually lead to bacterial and fungal infections, white spot, fin-rot and other diseases that take advantage of compromised immunity. High nitrate levels are often the cause of excessive algae growth too.

The level of nitrates tolerated without ill-effect varies from species to species, but as a general rule-of-thumb the level in the tank should be kept as low as possible: ideally below 40ppm. Some species have a particularly low threshold for nitrates – Fancy Goldfish need levels below 20ppm as higher amounts can cause buoyancy problems which are frequently mistaken for Swim Bladder Disease. Where fish have low nitrate tolerance, care sheets will usually indicate this.

Water should be tested weekly using an aquarium nitrate test to monitor the level so you can be ready to take appropriate action when levels rise.

How do nitrates get into the water?

Nitrates are the end product of the nitrogen cycle. Any aquarium with life in it will accumulate nitrates as a natural consequence of the filtering process. Standard filtration does not deal with nitrates and they must be removed by regular partial water changes. A typical freshwater aquarium with the correct amount of stock, efficient filtration and correct feeding will need a water change of around 25% every week to keep nitrate levels in check and to replenish essential minerals and trace elements in the water that have been consumed by the tank’s occupants and plants.

Nitrates are usually present in the tap water used to fill the tank. The level varies with the source of the tap water, but in the UK must be no more than 50ppm by law. Most UK water suppliers provide information by postcode on various aspects of water quality for the locality, including the average nitrate level, but because this can still vary it is advisable to use your test kit to establish the nitrate level in your own water supply.

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