the fresh air is a good idea. I don't have a ca reactor. The probes are calibrated frequently and were just replaced recently. I do run the refugium on a reverse daylight cycle but it doesn't seem to matter.
I hear you about worrying about the big three only, but I've always found that when I do manage to get the pH up, the corals have always responded well because of it, look healthier and have better PE and growth.
I think I'll set up a kalk reactor for top-off.
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