Your pH is essentially regulated by ambient CO2. With sufficient buffering capacity (dKh), which you have, there is nothing you can add to your tank that will cause a shift in pH that will last more than a few hours. With your Ca as low as it is, I would suggest your coral loss was as a result of insufficient Ca. IMO, your alkalinity is fine (8-12 dKh is often quoted as a desired target), but getting back to your original question of pH... I would offer three potential explanations, and IMO, they are the only three. Either your test kit is wrong (my vote is here), you have a million plants in your home that are sucking the CO2 out of the air, raising the pH of your tank, or your top off water is strongly basic (high pH). If your top off water has high pH, let it air out for a day before using it (you should be doing this anyway to allow the chlorine/chloramine to off gas), your tank will drop back down to normal pH on it's own. If your house is full of plants, you would expect large swings on pH from day to night as your plants switch between CO2 uptake and release. If your test kit is wrong then there is no problem. Really, just stop testing for pH. If your dKh is testing above 6 or 7, your pH will be fine. I think if you ask around, you will find people would say your coral loss was due to insufficient Ca. Rectify this by raising it about 20ppm/day and you will be fine. You can spread the dosing out with your doser so it will not ppt out on your pumps. I think you would be fine to even raise it by 40 ppm/day if you spread it out over several doses, but that's just me. Good luck,
Dan
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