SPS Growth Puzzle
 

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?

What type of bulbs are you using (Manufacturer)? Are they 10K, 14K or 20K?

I find Ushio and Geissman bulbs to be the best, and I use 10K for highest/optimal growth.

what kind of lighting? up your water changes and bring your calcium and mag up. I find growth accelerates for me when my cal is 440ppm and my mag is 1400ppm. Also feeding helps so much i terms of growth but sometimes can be detremental to the color of the corals because of the increased nutrients.

Bulbs are AquaConnect 14k, one blew yesterday and I'll be switching to Radium, which I used for years and liked. The tank is a shallow 90, so the reduced output of the radiums should still be sufficient.

Lighting above. I've found that anything over 380 for Ca is fine, as long as it's maintained. I use a big a$$ Ca reactor that keeps it about 400. I don't worry about Mg, but did test it a couple of times and it was 1400ish. My previous setup used IO and no supplements other than reactor.
I never found feeding to help or hinder, other than brown out the corals if I over did it. I can see feeding helping a bit, but this I think is more serious. For example, I have a frag that I mounted 2 years ago, 2 inches long. It encrusted, and nothing since. That's just wrong :)

How far off are the lights? Maybe you're getting some photoinhibition going on?

it's not the lighting. I get 1-2 inches of growth in my sps per month. I can only tell you what works for me. Calcium above 420ppm and if i dont add mag often then growth stops. IO salt hasa very low mag and coraline algae just rapes the stuff. I feed with coral frenzy and it really does help for growth. I feed once a week maybe twice if i am bored. Its not going to be a one thing fix, its probably a mix a few things added together that is hampering growth.

What type of corals are we talking about? like are they maricultured corals or frags from someone else?

from my experience, i won't be buying to many maricultured corals anymore. mostly because of the fact that they just don't grow for me compared to frags from snappy, fishytime, wickedfrags and so on. All they did was encrust and maybe got an inche out of one in a year while my frags are now colony size on 6-8 months.

I thought that might be happening, so swapped in a set of used radiums for 2 months, no change.

I've got frags from Christy, Snappy, Denis, etc, all the same. And not species specific. My birdsnest has only grown slightly, where compared to the same coral in a previous tank it grew like crazy. My caps are not too bad, some growth, but not what should be for 2 years. Even digitata is slow growing.