Why are my nitrate / phosphate readings low?Updated 2 months ago

When we measure the water for nitrates, the reading is the residual level after plant absorption. Plants do not need a constant excess of nitrogen to grow well. Even in tanks with fish, it is actually normal and healthy to have zero NO3 readings- it is one of the ‘secrets’ of keeping algae under control.   

A standard daily dose of APT3 adds less than 1.6 ppm of NO3, and most well planted, mature tanks with moderate fish load easily takes up that amount every day. 

So when we measure NO3, it reads zero. (This can be shocking to EI users!) These tanks all measure zero for example.Most of the tanks at the 2hr gallery measure 0 or close to 0ppm Nitrates in the water column 24hrs after dosing. For tanks with aquasoil substrates, the substrate also serves as a long term source of nutrients to draw from.

On the other hand, it is difficult to measure Phosphates accurately. This is because it binds to organic matter and substrates. In other words, measuring a low value does not mean there are insufficient phosphates. If you dose APT 3 regularly, you have enough phosphates in the aquarium.