I used to check them daily but now every 3 days I do since it's as worrying like before.Oh that's for three weeks? Not daily? ok.
My OPINION is, check alk daily for a few days. Calculate how much is lost, and start dosing if it's a big loss. I don't lose that much alk probably cause I do 25% water changes at least once a week on my tank. But mine is smaller than your's and I can replenish easier with water changes.
You might have to start dosing though. Your alk might be ticking off that one coral, and it's just your first sign before the rest are ticked. Remember, it's not about survival, it's about thriving. I have seen mine do some crazy extension where I end up surprised how big they got. The fish...who know whaat it was besides the ich. But do your cycling thing, check your alk and dose if needed and you should be good. I'm excited to see how it goes!
I will do larger water changes for now on to get anything that's in there out but will do it at around 10% every 2 days until I reach 100% of water volum maybe then the issue will be fixed.
Thanks a lot buddy for your advice and will up date you on how things goes and what i did even if it didn't work