Ammonia

This is the top cause of fish death in aquariums. In an established aquarium, you should conduct an ammonia test and record it in a log once per week. Whether you own a saltwater or freshwater aquarium, the ammonia level should be 0.0ppm or undetectable. While a test kit could be used, you can also install an ammonia alert sensor.

Anytime a fish falls sick or deceases, be sure to check the ammonia levels in the tank for their cause of death.

Nitrite

This is the product of the breakdown of ammonia, and is also toxic as a result, should be in concentrations no greater than 0.0ppm. Include nitrite testing in a monthly routine, as nitrite levels may fluctuate in ‘mini-cycles’ from time to time. If there is elevation in nitrite, it could be a sign of problems brewing in the tank.

Nitrate

This is the product of the breakdown of nitrites, but isn’t particularly dangerous. However, do watch for increased levels, as they could become toxic and stress fish. For freshwater tanks, nitrate should be kept at levels below 40ppm, with saltwater tanks generally requiring lower levels. An appropriate filter media and regular water changes are usually enough to keep nitrate levels down

pH

pH levels should generally be around 6.5 to 7.5 for freshwater fish, while saltwater fish may thrive in a pH upwards of 8. Do remember to do research on the pH levels required for your species of fish. A pH alert sensor can be used, alongside a test kit, to ensure that pH levels are kept at an appropriate range.