For me i make use of diy co2. pH of my crs tank will shoot up. But I uses my diy co2 to maintain it at mid 6. I put the diffuser near to the water surface to reduce the amt of co2 diffused into the water. Don't know if it works but its looking fine for me.. Yup.
As for my TFR/Sakura tank, I experience too low pH. So I added in some coral chips to bring up and maintain it.
As for my sulawesi, I used coral sand.. so not much problems with the pH.
But if it's a real sudden spike, look out for things that caused it to spike. I'll usually make water change and monitor it closely.
If still cannot, I'll use my lifeline and CALL FOR HELP! lol..
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