When I had the betta in the tank, I tried blocking off the slots with a very thin piece of filter sponge and the water level dropped way down where the filter sponge is. So, I took that off. He liked to sleep stuck to the slots and was tearing his fins. If I used some sort of craft mesh, I think it would have to be really fine to keep chili rasbora - or whatever tiny rasboras I have - from going through it.
I think there is pretty good flow going from the tank through the slots into the filter, even with the pump on the Low setting. All the loose pieces of foliage that come off the plants end up stuck to the slots, or going through the slots and I find it sitting on the top of the filter sponge. I tried growing red root floaters and they were always being sucked in.
I just did the water change in the larger tank where the rasboras are - Don't think I will be catching them.
I guess that was pretty naive of me to think I could in a heavily planted tank. Crafty little guys. All friendly and fun and up to the glass till I brought the net into the room then, ZOOM
What rasboras? I don't see any rasboras!
So I moved a half dozen of the small cherry shrimp females in there to have something to watch, and since an Oto was hanging on the glass, grabbed him too, since I've a little bit of diatom in there. He can clean that up and then if he's acting stressed, I'll move him back to the bigger tank.
I've heard the shrimp can move back and forth in the slots between tank and filter without a problem - so we will see.
I have been looking up what fish I can put in there other than a betta with the pygmy corys. CPDs are pretty, but I'd need a school and they sound shy. I read that a dwarf honey gourami might go after the corys.
Would Harlequin Rasbora be big enough not to go through the slots, yet a good size for the 5 gal? The Endlers didn't have a problem being sucked into the slots - well, as far as I know.... I did take the filter out and search for the two missing ones in there and didn't find them.
If I could come up with something to cover the lid's opening that would not block the light, I might get more Endlers if I can't come up with something else. I tried plastic wrap (kitchen) but to much moisture condensed on it.