Rainbow shark and new fish

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.

 

u can add new fish as long as the don't have red fins or red bodys apart from that u can add new fish cheers john

 

your welcome

 

You can keep small, peaceful schooling fish without too many bright colors.

 

If you have him and the pleco do not get any more bottom dwellers, he will get upset.
How big is he???
I have 3 rainbows...2 baby albinos in my 55,which is a no no...I know.
And my common rainbow in my 28 gal..
I had him in the 55 but he is a big jerk and was trying to claim the whole tank.....hes calm in my 28 which has more fish in it than my 55....honestly I think it's the gravel...in the 55 gal my gravel is dark and brings out more colors..in my 28 the gravel is bright yellow and blue green....I think it makes him feel intimidated, I dunno....