Where's all the nitrates?

[binhluque]

Hi, I've been taking care of a betta in a 6.8 gallon tank for a few months now. The tank and water are well cycled - I use an API freshwater master test kit, and never get ammonia or nitrites.

I do partial water changes when I can see excessive amounts of poop on the bottom. The reason I don't change water more than that is, I keep getting nitrate level test results between 5 and 10 ppm.

So my question is - where is all the nitrate going? Even after a partial water change, nitrate level tests show between 5 and 10 ppm. Over a period of two to four weeks, this measurement doesn't change.

I follow the test kit instructions carefully. I know that not shaking the test solution a lot is a common mistake, and not shaking the test tube a lot while mixing both test solutions is also a mistake, and both of these mistakes can cause inaccurate test results. So I figured that out back when I wasn't even getting a result above 5ppm.

So now I shake like crazy and wait 5 minutes before comparing the test tube to the color guide on the back of the booklet. I expect that from one week to the next, I should be able to see nitrate levels rising but that basically never happens.

Anyone know what's going on?

The fish seems healthy, I really don't believe that nitrates are building up to unhealthy levels. And I do change water when I can see the water is looking too dirty (too much poop on the bottom). But I've been going three and four weeks without doing water changes, and then I'll wind up changing maybe 25% of the water, because that's all it takes to suck out the worst of the poop.

So where's all the nitrate going? Why am I not measuring nitrate levels increasing?

 

[seangee]

What plants do you have? Plants will use nitrate as "fertiliser".

 

[Byron]

Agree that live plants will minimize nitrate, though it is actually not so much that they use nitrate, but that they take up so much ammonia/ammonium so there is much less nitrite and thus much less nitrate in the end. Plants use ammonia/ammonium faster than the bacteria.

What you see could still occur without live plants. There are denitrifying bacteria primarily in the substrate that use nitrates. This is why you do not want to be too thorough in cleaning the substrate, within reason though obviously.

Nitrates do negatively affect all our aquarium fish. Some are more affected than others, and the level of nitrate plus the exposure time also factors in. But we must always recognize that like ammonia and nitrite, nitrate is still toxic. Keeping nitrate as low as possible is always better for the fish. My tanks, which are all planted, run in the 0 to 5 ppm range, and have for years. I rarely test nitrate, but when I sporadically do, it is always in this range. And I always test before the weekly water change.

Some think that water changes should be based upon nitrate, but this is not good. If you see nitrate rising and then do the water change so it lowers, you are causing problems for the fish from the higher nitrate level. Performing a regular (meaning once a week on the same day) and significant volume (meaning 50-70% of the tank volume) water change should keep nitrate levels consistent from week to week, and that is what you want, with the level as low as possible.

 

[binhluque]

There aren't any live plants except for a speck of algae here and there.

 

[Byron]

There aren't any live plants except for a speck of algae here and there.

My previous advice still holds, plants as I said therein were one factor but not major anyway.

 

[binhluque]

Thank you Byron, that's helpful. Was just answering seangee's specific question.