That is what it is...I little almost self sustaining ecosystem. Mine doesn't have a light but it is sitting right inside a north facing window so gets a lot of natural light.I wonder if the problem is keeping a culture of snails with the predators. You'll have to feed the the tank enough to keep the snails going. Catch 22.
A plant growing out of the snail tub could dramatically control the ammonia and nitrAte. Plus floating plants. I use soil bottoms (let it cycle) whenever I was ever trying to keep snails. The soil holds a ton of bacteria for me and keeps my softwater buffered. I don't even necessarily use a filter, but some water movement would be best. You could even plant it with low light easy plants and use sunlight. Essentially a little ecosystem if you get the right balance.
I forgot to mention that I also have crushed coral, a piece of cuttlebone and seashells in my snail jar. I have no substrate in it. For me it is easier to clean up the piles of snail poop with no substrate. I have fairly soft water and know the snails need calcium to grow strong shells. I usually don't keep an eye on the perimeters other than the PH of the snail jar. The few times I have checked I have never had an ammonia reading. I am thinking the Pothos roots must be keeping it in check. I do a 75% water change every other week or so.
Your snail tank shouldn't need any kind of fish in there with them. Hopefully knowing now how I do mine and how angelcraze does hers you will be successful should you decide to try again.are you talking about why I had issues with a snail tank before? if so, I think the issue was that there was no fish in it so the snail died. so I may get a few guppies or something for the tank if I do this to keep something else other than snails in it. I didn't have real plants in it last time either so i'd likely add a plant to it as well.