I have 3 fish tanks two 125 and one 55 all mostly cichlids with a mix of catfish and sharks.
Albino Tiger Oscar 7 inch
Electric Blue Jack Dempsey 5 inch
Pink Convict 4inch
Blood Parrot 4 inch
Four Line Pimelodus 8 inch
Tiger Oscar 5 inch
Gold Jack Dempsey 4inch
Firemouth 4 inch
Black Shark 8 inch
High Fin Plecostomus 4 inch
Electric Blue Acara 4 inch
Albino Rainbow Shark 3 inch
Albino Bristlenose 2 inch
I originally had just the two 125 running the Acara was in the first tank but he was being chased and getting cornered mostly by the convict and Dempsey. I didn't want to lose the acara so I tried moving the acara to the second tank rearranging decoration and adding new hideaways giving him a chance but the oscar and the firemouth in that tank was bothering it too much. So I started a 55 gallon had it running for three days, took some bio media from my fluval filter and added to the new tank filter just to help with the cycle, than added him in, added quick start for seven days. It's been two months tank is fine, but he is always hiding in his cave only coming out to eat than going back. In the other tank he used to be out and about swimming around. I got everyone when they were babies 1 inch to two inches so that is why they got along to begin with and over time when the cichlids got bigger they got more aggressive mostly to the acara. I got a albino rainbow shark and albino pleco to keep him company thinking maybe if he sees other fish he will come out himself. But the other two hide as well, I was wondering what else can I put with the acara that can help him be more bold for him to come out more, he is not that aggressive.
Will these fish work
Gourami (Blue, Gold, Opaline, Kissing)
The Blue Acara is generally peaceful with other fish of similar size, but can get territorial at feeding time and when breeding.
Angelfish would work with a Blue Acara as long as the Angels are larger than the Acara. No Gouramis as they can be more aggressive than Cichlids. Denison Barbs would work as long as they are close to the same size as the Acara, and they are both close to the same size as adults. You could also get a few more Acaras and have a species only tank.
I would also check your water parameters to make sure poor water quality isn't the problem. Also make sure the water temp is not too cold, it needs to be about 80 degrees. It is unusual that a Rainbow Shark and an Albino Pleco would hide, unless there is a problem in the tank.
Hope this helps you, good luck!