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Mike offers some great questions. Your NO3
source is coming from somewhere. Given the fact that you have a small bio-lad (in terms of fish) I would turn attention toward food, feeding schedule, source water (for top-offs and water changes) and maintanance routeen.
GHA is ussually a sign of excess nutrients in the water. Check for PO4
in both your tank and source water. Again, evaluate what and when you feed the tank. I suggest using a high quality source water and doing several partial water changes to help with NO3
issues. As far as the GHA goes...try removing as much as you can manually during the water changes. It is likely your corals are reacting to the PO4
rather then the NO3