Stocking 90 gallon aquarium

6 chromis IME dont last in a 90. Ive tried a couple of times and have been left with 3 each time. So Im stuck with 3. but 3 is perfect for a 90.

 

I personally think you're on the higher end of healthy stocking levels. I would try a smaller group of chromis, or at least probably expect that they will whittle their group down to a smaller number, which happens with quite a lot of groups in a lot of tanks. If you do some searching on 3reef and elsewhere you'll find lots of issues keeping groups of chromis successfully, despite the fact that there are lots of people recommending them as good shoaling fish. Maybe it's just because they're cheap.

Also I do think that the yellow tang will eventually outgrow a 4' tank, it may take a few years but just be prepared for that, and also I would recommend adding it last as they can be territorial as well. I think there are better options for a 90g tank if you want to have a tang though. Check out the Ctenochaetus genus, like a Kole or Tomini tang. I think they are much more suitable to a 75/90g tank.