Actual numbers for the parameters will help us diagnose what is going on as well as how many bulbs this t5ho unit is.
Corals shrinking can be a parameter issue, caused by higher nutrients or low alk
It could also be lighting as well, like already mentioned. How long have they been under this light fixture? How old are the bulbs? Over 6 months can change the color spectrum and cause issues, including algae growth.
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