Water Parameters

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What are you feeding the fish? how often? This might be the cause of cyano if you overfeed?

Otherwise, you might try some other foods or phytoplankton (DT's) for boosting your corals. My tank is not quite that old, some stuff does well (zoos, mushrooms, yellow polyps, open brain) and some is slowly (several months now) dissappearing or shrinking (cabbage leather and finger leather, Acropora frag).

I have same water parameters as you and decent coraline growth also. I have 192W on 33g, what is you light and size of tank?