Parameters very skewed...

[Eel Freak]

Hi!

I have a 205g tank that I've used Reef Crystals on for almost two years. I've kept LPS, clams, anemones, etc. without issue. However, I've recently taken a stab at Acropora. I had a Phosphate issue that I took care of, but now I'm dealing with low alkalinity (7dKh) and high calcium (around 500ppm). My giant Table Acro has burnt tips, but now is extending its polyps since my phosphate correction. I also have an ORA Acropora nana that is not extending it's polyps to a full extent...

Tank stats:
200lbs live sand
200lbs LR
200g (96"L x 24"W x 20.5"H)
2 - VorTech MP40w's for flow
Iwaki MD-70RLT return thru OM 4-Way
SRO-XP5000e skimmer
3x 250w Elos SpectraChrome 20K lamps, 12hr photoperiod, lamps 4 months old running on Galaxy ballasts in Reef Optix I reflectors

Temp: 79-81
NH3, NO2, NO3: 0ppm
PO4: around .25ppm now, dropping...
Alkalinity: 7dKh
Calcium: about 500ppm

Based on where the tank is now, that really only leaves the salt as the apparent reason for my out of whack parameters/failing Acropora. What do you guys think? I have various Montiporas, a Derasa, Maxima, Euphyllias, etc. that all are thriving...

All input is greatly appreciated. Thanks!

[sporto0]

What about Magnesium? 2 years is enough time for inhabitants to use up elements that your salt can't replenish fast enough. Do you dose? How often do you do water changes? I use reef crystals & have no problems at all.

[Eel Freak]

I haven't a way to test for magnesium yet....

No dosing.... Never needed to as all I kept did well until now...

20% every week. Sometimes I miss a week though.