Here we go again, earlier I posted this same question but about a 10-gallon tank. Then I lucked out and one of my co-workers gave me his old 20-gallon. So here we go again. I still have the 10-year-old plecostimus, flatulent 6-year-old loach, a foul-tempered 7-year-old Giant Danio
, and two ancient purple passion something-or-others that I think have dementia. The eel went to the big pond in the sky, so he's not going to be a problem.
So now the arrangement is the Danio and two elderly what's-its will stay in the 10-gallon and the plecostimus and loach will cycle and stay in the 20-gallon. I already have my bamboo, lillies, and apogenium (boy am I spelling that wrong) bulbs started with fertilizer in the 10-gallon. Now, how many female bettas can live in a 20-gallon (yes, with lots of plants and hidy-holes) and what sort of tank-mates can they tolerate if any? That's a real issue because my two males each have a snail and a dwarf African frog living with them in their 1-gallon tanks without problems, but I once had Renoir in with some danios and he ate any that he could catch.