Welcome! Glad you got back into fishkeeping and found this place. It's awesome! Lots of helpful people here.
Are you familiar with cycling a tank? Sounds like you are but I just wanted to make sure.
And the 1 inch of fish per gallon of water rule (of thumb)?
You could probably squeeze in a small school of tetras or something. That's what I have in my 20g (listed below in my sig). Or some bottomfeeders like cories. Or maybe otos to eat your algae. Good luck!
Edit: If you're anywhere near Phoenix, AZ you could have some of my cories that I bred.

Teehee.