So you are telling me that zoas or any coral will grow over rock that has algae on it?
So my thoughts, when your tank was a FOWLR did you use copper to treat the tank, also is the LR you have in it the same rock that was in the FOWLR? If so your rock may have absorbed copper/phosphates from the water column and is now releasing it into the tank.
hope you find your problem
I'm not sure if you are aware but your alkalinity is very low. It should be between 8-10 depending on your other levels. Since your magnesium is fairly high, I'm guessing your zoas and having a hard time taking up calcium and magnesium since alkalinity is so low. Do a water change with a good quality salt water at 1.026. Then check your parameters. You may need to dose alk if you aren't doing a weekly water change.
I'm not sure if you are aware but your alkalinity is very low. It should be between 8-10 depending on your other levels. Since your magnesium is fairly high, I'm guessing your zoas and having a hard time taking up calcium and magnesium since alkalinity is so low. Do a water change with a good quality salt water at 1.026. Then check your parameters. You may need to dose alk if you aren't doing a weekly water change.
What kind of salt are you using?
I have been using IO for the last 4 or 5 water changes and it is working just fine for me. I was using real ocean water but was tired of the LFS being out of it all the time some I got a RO system and was recommended to use IO by the person I get most of my corals from. Your problem could be from switching salts and the corals are trying to get used it the new salt.
So you changed your bulbs and your salt in a 3 week span? I would stop changing things around for a while. Let the tank get stable and adjusted again. Good luck.
~Dee~