I would check to make sure your rodi water is 0 tds with a hand held meter. Seems silly but my inline meters failed recently and it caused big problems in my tank.I’ve had a reef tank for more than 30 years and have had acros for around 15 years. I’ve never seen this before. Starting about a month ago, several of my large healthy acros started turning white around their bases. Slowly, the white grows until all the coral’s tissue is gone. It started with a metalic pinkish-yellow milli that I’ve had for more than 8 years. I fragged a large piece of that and put it next to a large red planet colony. That frag was the first to show symptoms and die. The red planet then got it. Then 2 colonies of garfs got it. Now, corals all over my tank have it. I’ve had to emergency frag several corals that I’ve had for many years.
This issue doesn’t seem to affect birds nest, encrusting corals, clams or a few others, but most branching acros and millis are affected. I initially thought it was due to a contaminant in the water and made multiple water changes, but the plague e continues to spread.
The strange thing is that the corals are all still growing and showing good polyp extention and color. I’ve tested my water multiple times. Alk around 8.5, PH 8.3, and all other parameters are perfect. The corals aren’t starving.
Any help would be appreciated.