Hi and welcome,
Critters like different things that make them grow.
Your tank has certain things in it that lets some corals do fine, but polyps don't. The problem I have found is that if I tweak the water to satisfy one type of critter, the ones that were doing good take a nose dive.
There are so many wonderful things to place in the tank. If Polyps don't do well in your tank, just stock the kind of corals that do.
Also I have some advice. I am not the grammar, or spell police, but... My spell check won't work on this site, I can't fix the thing, so I keep Microsoft word running in the back ground, and before I post, I copy paste my response or question and spell check it that way, then paste the correct version back on the reply window. It takes only a few seconds.
I am dyslexic and I don't like being made fun of for my spelling or writing a word like, t-h-e to look like h-t-e. Also it helps others to understand what I am talking about.