Hello,
The most important thing to do which others have expressed is test your alk, and other parameters. Having 0 ammonia and nitrites is good. Having zero phosphates and nitrates is not good at all. Your alk should be at 8 and cal at 440 and all tanks vary. But generally speaking it’s 8 and 440 for those. Make a trip to your lfs and have them test your water, if you have none try the local aquarium. If you don’t have either option, you should be keep this on hand for such situations. Corals usually react to something that has happened days or weeks ago.
Pics would help, do you have sps, lps softies etc. Are any of the fish (if you have any) reacting to this? I would also dim the lights, (which ones do you have, I saw it was mentioned sooner). You have to raise alk and cal SLOWLY because it will also have to large of a swing and kill your corals.
Try and place your lights back on acclimation start something running carbon only and personally I would stop the gfo if phosphates are at zero. The corals need food and your water is too clean and your starving them. I would also as you slowly raise your alk and cal I would feed your corals with reef roids or marine snow.
Curious -why lower the lights? Doesnt that just add another variable that will need to be addressed?
