natural tank

[Phoenixphire55]

I know natural tanks aren't really very popular but I have a little 5 gallon natural tank (no filter, sunlight, fluorite substrate). I'm wondering how often I should change the water. Since I'm not using any fertilizers I'm depending on the betta's poop to provide nutrients to the cabomba plants that are growing (or "growing") in the tank. However, the plants dont look so hot lately so I'm not sure whats wrong and I want to do a water change...but will that remove most of the nutrients from the tank? I have volcanic rock in the tank as well and the rocks were from fully established tanks, so maybe the nitrogen from the poop is being converted by the bacteria and leaving the plants with nothing to eat? I dont know..

 

[Purrbox]

It's not so much that natural aquariums aren't popular, as there aren't a lot of members that have them on this forum.

I think the issue is that you've setup a natural aquarium with Flourite substrate. Everything that I've read about natural aquariums involves the use of soil as at least part of the substrate. Generally this soil is treated to remove most of the organics that would rot too quickly and cause algae issue, but the rest will slowly degrade releasing nutrients and carbon to the plants.

Generally you'd be doing very infrequent water changes with this type of aquarium, definately no more than monthly and I've heard of going as long as six months between water changes.

Plants can make use of Ammonia, Nitrite, and Nitrate, so the bacteria aren't going to be making the nutrients unavailable to the plants.

I suspect that you are dealing with some sort of nutrient deficiency. I'd probably recommend replacing your substrate with a soil substrate, or at least adding a soil layer under the Flourite. If you don't want to do that, you'll probably need to look at supplement the aquarium with fertilizers (root tabs and/or water column). In that case it'd be helpful to nail down the specific deficiency to determine what you need to add.