SPS Growth Puzzle

[Aquattro]

Fencer, agreed, and all my parameters are there for success. While I would prefer a wavebox, my tank won't work with one so I'm stuck with Tunzes. However, I've always used them, and bigger ones, with great results. I've used both sand and barebottom, both equally well for growth.

My approach is to try and find what's different this time around. I use a different RO membrane, it's been a constant (prolly needs replacing now). I also have about 30' of flex pvc tubing, which I've never used. Sump is new to my system, maybe it had something in it?
Tank is new, but it was used and had a successful reef in it. All other equipment is my old (successful) stuff.
My photoperiod was reduced to 6 hours/day, I've increased it, but 6 hours of 400w should suffice. But I've increased it just in case.
I feed PE mysis and pellets, just like always.

I've used zeo and not used zeo (full system), with only an increase in color.
I use carbon, 1 cup/month
My default levels are good, and doing bi-weekly water changes should more than keep up with consumption.
I have to say that I have better colors now than I ever did in my old tanks, I'd just like to see it fill in a bit