I have a 6 gallon tank which I've been using as a betta tank for some time, with only plants (Elodea) as filtration, and no substrate. I've been regularly changing around 50% of the water a week and generally trying to take as much care of it as possible. I've asked about whether it's ok to use plants instead of filtration for a 6 gallon betta tank on here before, and have been told 'yes' by some very experienced fishkeepers.
But unfortunately, the same thing has happened to all the bettas I've kept in there - they've started off incredibly happy and healthy and their colors have improved massively from how they were in the pet shop, but after a few months they mysteriously begin to get lethargic and stressed-looking, and eventually die.
I can't figure out why this is happening!
Certainly everything goes very well for a few months. I can't understand the eventual decline. Unfortunately I can't afford a nitrate/nitrite test kit - they are INCREDIBLY expensive and I am broke - so I can't tell you what the levels of these toxins are in the water. However, I have noticed that the pH gradually gets more and more acid in the tank, despite my substantial weekly water changes.
I am thinking of getting some gravel and more plants for the tank (namely java moss and cryptocorynes, and some floating Java Fern to replace the elodea) to provide a subtrate for beneficial bacteria, but I don't know if that would solve the problem.
While I'm at it, any ideas about suitable fish (apart from bettas) for a tank this small (assuming I ever work out how to stop them dying)? I love small shoaling fish but please don't suggest corys as I've had a lot of bad luck with them
P.S Since this post is full of a lot of bad news, I thought I should add something positive as well..my main tank is absolutely flourishing at the moment, despite greatly reduced numbers of fish (or perhaps because of that!) and I'm looking forward to replenishing my supply of Cherry Barbs eventually. For those who don't know, the main tank fell into decline and a few fish died after I had a lapse with my water changes. Lesson learnt and water changes regularly every Wedensday now :)