I know the feeling! Harsh but true.

The tank just has to cycle and finish before any more 'toys' are added.
Especially since these 'toys' are living beings.

The pleco is wrong for the tank. I do not have one even in my 70G tank (did
at one time, found it a good home luckily enough). A dwarf catfish would
work but no more than that and only once the tank is done cycling. Due to
the damage he has done, that may require a complete cleanout of the tank of
all the chemicals and drugs.

Neil, you almost need to start over. Do not get any more fish. Take the
pleco back to the store.

Swap out 50% of your water and most of the gravel, then let the tank
natually cycle. It will turn milky-cloud white for about a week. Thats
normal. Do not use chemicals to clear the water at that stage. Just let it
ride. You will end up with a crystal clean tank that is self maintaning
almost, if you do not overload it.