never as already stated. Every fish u add is adding 2 your massive amount of maitainence on the tank. At a certain point your fish will develop problems.

with the fish you already have adding more will only lead to problems in the future.

I found this out myself just after i started fish keeping myself years ago. I had great friends and since i was enjoying the tank whenever they came to visit they brought more fish for me. I had a 20 gallon but after 3 months ended up with 15 fish of various types. Woke up one morning to them all dead.

Do not add more fish unless you find new homes for some of the ones you already have.

I have a 55 gal myself and a 10 gal. my 55 has 2 ropefish, 4 jewel cichlids, 1 black ghostknife, 1 chinese algae eater, and 2 rainbow loaches and i do not dare to add more fish which is why i set up the 10 gal for a few more fish. The general rule is 1 inch of fish per gallon but i do not go by that rule myself. After personal experience you need to check out temperaments of fish because in my opinion alot of fish need more room than that in the tank to survive and do well. My mix of fish isn't so good temperament wise but i have been lucky and it took me 1 and a half to 2 yrs to get this mix of fish.

With the mix you have i wouldn't dare to add more fish. If you want to keep them add another tank to the house and split your stock between, only then would i consider adding a bottom feeder.