helenf

I have an idea about this, but would like to learn other people's experiences and opinions. If you have had an experience like this, please let us know what yours was.

I'm comparing two tanks.

5 gallon NPT: Soil+gravel substrate, heavily planted with fast growers (hygros, ambulia, duckweed, elodea, a crypt is growing magnificently, etc). Moderately heavily stocked with a betta, male endlers, a few shrimp, an apple snail. Only circulation is an airstone running slowly. No filtration.

30 gallon coolwater community Gravel substrate, heavily filtered, lots of oxygenation and water flow from the trickle filter, heavily planted with fast growers (mostly elodea and different hygros, plus slower growing anubias and java ferns). Added DIY CO2 and tracer fertilizer. Moderately heavily stocked with goldfish, siamese algae eaters, female endlers and fry, white clouds.

The temperature of both tanks is about 23 degrees. Both always have zero ammonia and nitrite. The nitrate level of the NPT is 5ppm. The nitrate level of the other tank is around 20-30ppm, with 3 or 4 10-15% water change weekly (I change a bucket out every other day, basically).

Now, I think that I feed the NPT less for its volume than the larger tank. I certainly take out much more plant cuttings from the larger tank, for its volume, as the growth in the larger tank is much faster (the elodea, in particular, grows a few cm daily since I added the CO2). But the nitrates in the larger tank are a struggle, whereas they are not a problem at all in the NPT.

Why the difference in nitrate levels? Surely less food + faster growth should mean the nitrate levels in the filtered tank would be lower, but they are anything but!

I do have some ideas, but I'd rather hear from other people first, if you don't mind. So what are your experiences comparing NPTs with your other, filtered tanks?