A 7" peacock eel is a stunted peacock eel if it's in a 20 gallon. Wild caught or captive. You need to ditch the eel. I understand wanting one, but you just can't have those fish together in a 20 gallon tank. I know that's the stated minimum for all those fish, but I've talked to people with peacock eels... Both wild and captive. They all started off with them in a 20 gallon, and all wound up upgrading to a 100-150 gallon because the fish got huge in a short period of time. I promise you... 7" is bare minimum STUNTED.