Add me to the list that disagrees highly with keeping a betta in a 1g.
As for what you could do (some random brainstorming):
Hope that gives you a sense that you do indeed have possibilities. In the meantime, if that tank is cycled but your fish is dead you need to be sure you get some ammonia into the tank (at least a tad) otherwise your good bacteria are going to start dying off.
As for what you could do (some random brainstorming):
- Plants only. Maybe use the tank to grow/cultivate plants and then as they get larger transfer them to one of your other tanks
- Culturing live food, as someone else already suggested. I hadn't thought of that one myself but it's a great suggestion.
- How about a nerite snail? They can't reproduce in fresh water so no worries about a population explosion, and some of the nerites (like the zebra nerite, red spotted nerite, or horned nerite) can be quite colorful and very attractive. And nerites are easy enough to find, I think some of the folks active on these forums here sell them in fact.
- Or, alternatively, you can use it as a breeding tank for some other species of snails. Maybe pick one of the really colorful varieties of the European ramshorn snail. I myself have ones that are a beautiful tangerine/orange color (picture here), but they also come in pink, red, blue, and perhaps other colors. You could use the 1g tank to raise up the baby snails and eventually transfer the larger ones into one of your other tanks.
- A lone amano shrimp, especially a smaller one, might be an option too. Another cool creature.
- one or two Thai Micro Crabs. These are relatively new to the hobby and so there is not a ton of info about them yet, but these things are TINY. Full adults are only about the size of a dime (!!!), and as of yet no one has been able to successfully breed them (a pair will mate & have eggs, but the larvae seem to die a few days after hatching) so again, no worries about a small tank being overrun.
Hope that gives you a sense that you do indeed have possibilities. In the meantime, if that tank is cycled but your fish is dead you need to be sure you get some ammonia into the tank (at least a tad) otherwise your good bacteria are going to start dying off.