I think the issue could possibly be your magnesium level. I didn't see your test results.
If your magnesium is too low then your calcium can't fully saturate the water. So while it measure 420, your corals may not be able to use it. If that makes sense.
What is your coraline algae growth like?
If your magnesium is too low then your calcium can't fully saturate the water. So while it measure 420, your corals may not be able to use it. If that makes sense.
What is your coraline algae growth like?
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