Well, I'd say mine wasn't extremely slow. I fed beefheart as one of his meals per day, in addition to pellets, prawns, etc. and I thought he did fairly well. He outgrew my Jack Dempsey.
That's the good news.....however the bad news is today I found him behind my sump, outside my 150 gallon tank. I took the glass lids off for a few hours in order to caulk them into the hinges, and I don't know what happened. He was in there with a Firemouth and a few Plecos. There is nowhere to hid in this tank so I knew immediately he got out.
Good luck with yours. I think they're gorgeous fish.