Do you have plants or surfaces where biofilm could be growing besides the back wall?
How big are the tanks?
How many Otos?
What kind of Pleco?
I have absolutely no luck with Otos but I do know they need an established tank to survive and prefer to be in a herd (3 minimum I think) so the back wall may not be such a bad idea if there are no other surfaces for biofilm to grow on. Plecos are an entirely different matter. Some are wood eaters, my BNs are bio film shrimp food eaters and common ones are good for nothing except as a large producer of waste. Don't get me wrong, I loved my spotted sailfins when I got them at 3" but the constant rehoming as they grew and grew and grew, was a pain in the a** and if I knew then what I know now I would left them at the store. If you have large tanks(my last remaining one is going to have to move out soon to a minimum 180g)that they can grow into by all means have some but otherwise ..
We have a
38 gal bowfront with two hob filters (Aquaclear110, TetraWhisper20)
20 gal with two hob filters (PenguinBiowheel200, Aquatech5-15)
29 gal with two hob filters (Aquaclear110, PenguinBioWheel200)
gravel base in all.
(There is a mix of live plants (few) and plastic plants in all. Bought 10 bunches of staurogyne repens, and the fish have eaten all the leaves and left bare stems.) Have a few other live plants, a couple in each tank.
6 otos..2 per tank..little guys. Just got them about a week ago. ALSO bought 3 plecostomus a couple days before that. Actually it's a week ago yesterday for those, and all 3 died..One two days ago, another last night, and the final one today..? We have a 5" pleco (don't know the variety) that came with the original 5 gal.tank that got us 'addicted' to this hobby.He wasn't that large at the time. He is doing fine. Hides all the time,and sucks on the glass... but at least he didn't die us. (He is in the 38 gal.)
I KNOW we are very overpopulated in all tanks. It's ALL the guppies FAULT. I don't have the heart to flush them, and they keep making babies. We gave away about 30 of them, but have only had one 'taker' to our offer so far. We still need to get rid of at least 100...Any suggestions where to 'donate' them? We have no independent LFS, only the chain stores, and they won't take them. We ASKED. LOL. Thanks for your help....Laurie
P.S. Bought the otos last Thursday, and so far all 6 are OK.
P.P.S. We are kind of attached to our pleco. Thanks again for responding. L.