While they are compatible with discus, wild caught L183's are blackwater fish, needing soft acidic water and are very sensitive to nitrate. If you don't provide them with the proper living environment they will not do well. You'd be lucky to keep tank raised L183's in conditions other than blackwater but not wild caught ones. I don't know how long you've had them, do you know if they've ever been de-wormed. Wild caught plecos frequently have some sort of internal parasites.