I will tell you from personal experience. Flowerhorns are awesome. But, a 55 gal tank I don't believe is big enough. I bought one years ago. I didn't know anything about them. Store tried to sell me multiple lol. At that time I played about 50 bucks for it. Also got a red devil cichlid at the same store. No worries he said, they will get along fine. I got home and put them both into a 55gal I had a clown knife fish in. All were juvenile so it went well for a short time. Knife fish started getting beat up. Rehome it and then the devil as he became the only and next logical target. And eventually he outgrew his 55 and moved to his final home a 90 gal all to himself. We affectionately called him bubba. Because that's exactly who he was to any tank mates he ever had lol. With that said. I did place a 14 inch long pleco into his tank when it was far too big for the 55. Bubba would try to mess with him but couldn't get through his tough skin. One day the pleco stabbed bubba in the side leaving a nasty scar. Bubba and the pleco had an understanding since then. Moral of the story. They are monsters and a 55 may not be enough longterm. I would suggest at least 75 gallons. Just personal opinion.