[Aquattro]

So 2 + years into my tank, which is using most of the equipment from my old setup, my SPS have barely grown at all. Colors are nice, and I have polyp extension, but no growth. Some pieces have done nothing but encrust ( a lot!!). The best growth I've had is about 2 to 4 inches on some millies (in 2 years) and some pieces, nothing at all.
I'm all out of ideas, and at this point in the economy selling it seems useless, so I'm soliciting any and all ideas on what might be the problem.

Only thing I havent' done is replace the rock, which might be next. All corals are healthy, clams are good and growing, LPS doing well. I've treated for red bugs and inspected under a scope for any other pests. Temp is about 78-79, 2 x 400w at 7 hours/day. Water changes every month, sometimes use zeo, sometimes slack off, no diff either way. Ca was 390 last test, alk about 9. Don't usually check anything else, but never have. Run a big ER skimmer, tried a filter sock, and no sock, no diff again. I have a remote sump with flex PVC returning from basement, this is a difference from my old system that did well.
No sand in tank, lots of flow. Used Zeo salt for last year, switched back to IO for next water change.
Tank is 90g, sump is 125, total water volume 140g.

This is a big change from my previous 10 years of SPS keeping, where I had trouble keeping up with trimming frags out..

Anyone have any thoughts on what I might try next?