The questions asked are not meant to be overwhelming but instead are informative for those that are wanting to help find the solution. A fancy acronym will do nothing for you, stability is elementary and I think we can assume you already know that.
Things like the salt brand are important, Seachem is notorious for having a high borate content that tends to causes test kits to read on average 1.25 DKH higher than actuality! (especially when using Salifert test kits) The is especially true if water changes are often.
Because you are using Seachem salt you should be aiming for an Alk reading of 9.5 - 10 DKH thus resulting in a actual DKH closer to NSW or a little higher. Your tests that show about 6.5 may only be 5.25 DKH in actuallity!! (Not good!)
Knowing what you are dosing is also important, using ZEOvit or any other ULNS will result in "stripped" water over time, in other words, your system does not contain enough nutrients that the Corals need to thrive. Also when using these systems Potassium also gets low resulting in the need to supplement.
Ventilation is also important, a stuffy room with the windows closed can and will cause PH issues due the Co2 that builds up in the air.
Keep searching, an answer with stability as the advice will do you nothing, there is more to your problems that what has been assumed.
