That doesn't seem like very much light to me and I'm having a difficult time understanding how much flow you have in your tank. For many stoney coral you're going to want at least 30x your display tanks volume in flow per hour or 5400 gph however many people use even more than that. Alkalinity and magnesium levels are also very important so you should probably be checking them as well. Ideally you want alkalinity between 7-12 dkh and magnesium between 1200-1500 ppm.
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