Never any nitrate

Kieran said:

Hi, I’ve had my tank for 4 months now and all going well, it’s 300 litres and co2 injected. There are 24 x black phantom tetras, 17 Amano shrimp, 12 ottos and 6 doctor fish. Monte Carlo and hair grass carpeting is getting thick and lush. Zero ammonia and nitrates and since the tank cycled over 2 months ago I’ve never had a trace of nitrates show up on any test and I’ve tried from 3 different manufacturers. I have a lot of matrix in the canister filter I wonder could there be anaerobic bacteria living there which is converting the nitrate and releasing it as a gas and also the plants using up the nitrates View attachment 1054108
View attachment 1054107
. Any theories are welcome, thanks.

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Most likely not anearobic bacteria. How long have you had animals in your tank? Also, how did you cycle your aquarium?

It could also be just a well balanced system. Just because you do not get results on a test kit does not necessarily mean that plants are not able to use any nitrates, esentially being used at the same rate it is being produced.

The plants are probably using up the nitrates. I have 9 tanks at home (all low tech; inexpensive lights and no CO2). They are all from moderately to heavily planted. A few of them are also heavily stocked. When I test they usually have 20 - 40 ppm nitrates. The others are either lightly stocked, or just have shrimp. They rarely show any nitrates.

Unless you're adding fertilizers with nitrates, the plants are probably just absorbing and using all of the nitrates that the fish produce (well, nitrates that come from the nitrites that come from the ammonia that the fish produce), at about the same rate as the nitrates appear.

If you're happy with your plant growth rates and health, then great. If you start seeing algae or symptoms of nutrient deficiencies in your plants, you may want to consider dosing some fertilizers to provide more nitrates to the plants.

While there could be some anaerobic activity, it would be far too little to have an impact upon NO3 levels.

Since the type of plants you have usually do best under high light, I assume that your light is on the high side. As other posters said, your tank seems balanced (just enough nitrogen) …right now. The risk is that if any nutrients become limited (see Liebig’s law), things will deteriorate quickly. Could it be that you have an active substrate that is supplying all of the nutrients necessary?

Do you test for other nutrients (PO4, K, Ca, Mg, Fe, etc?). If it were I, I would want to see, at least, 20ppm NO3. No NO3 would make me concerned that it was limited. However, I don’t use an active substrate. Such substrates can keep your plants sufficiently healthy (until depleted) and water level readings may not be so important.