PH over 8.4? What was the Ph before? I would continue do another 30% water change to bring it down. I was going to recommend dose vinegar into your tank, but figured waterchange is a safer way to do it.
danmhippo, thanks for your reply. I will do another 35g change in morning. I'm out of salt til then. Corals look good but alot of powder residue. What should I use to bring down ph. Will it continue to rise. What should I expect from here?
Ike
The precipitate will subside in a few days. No lasting harm will be done as long as you bring your pH down to somewhat normal levels as Dan has advised.
Your nitrifying bacteria on on the LR, Sand and tank wall. If you have sufficient bacteria colonizing surface area and your tank has been established 6 months plus, large water change should not induce another cycle. Just make sure you don't disturb your sand bed.