The *tiniest* amphibians/reptiles/animals to keep in a tank?

Hello, I’ve just scored a 30 gallon tank for free, I’m interested in having frogs, crabs, snails, any type of little tiny creatures that I could put in there to give them a large space of a tank. I’ve always wanted to keep pets like this, but I feel bad for the larger animals kept in these small enclosures.

So basically, I want to find if there is an animal (or a mixture of animals that can coexist in captivity) that is so small that a 30 gallon tank would be a very large home for them! I do not care what kind of animal or how tiny they are, just no insects/bugs unless it’s food.

If it matters for legality or climate, I am in Philadelphia USA, it can get decently humid here, with average temps ranging from 10° to 90°F year round, but in our air conditioned home, the inside of the house would probably sit around 65-75° year round.

Bonus points for low-maintenence animals, but I am 100% willing to put in lots of effort to take care of whatever little guys y’all suggest! I just would appreciate some low-maintenence suggestions for when I travel and someone else may become their caretakers for 1-2 weeks at a time.

Thanks in advance! (If there is a sub that this post would fit better in/get more results from I’d be happy to be redirected there as well!)