I have had a rainbow shark in my 55 for about 2 years now. A few months ago, I had a small school of tiger barbs that i had to get rid of because they were nipping at my rainbow shark. My rainbow shark would always chase them away and become very stressed. Now that the tiger barbs are gone, my rainbow shark is very colorful and happy. Im ready to get some new fish to make the tank lively again. I was wondering if there would be problems with adding new fish. The shark has practically had the tank to its self except for two corys and a small pleco.