Yeah, I keep my Alk around 7, when I'm not concentrating it often falls below that. As mentioned stability is the key. Suggest u frag and do water changes. Get your mg upto 1300. It helps with the sps to assimilate the calcium and alkalinity ions. Everyone keeping sps some point will go through what's happening to u. I've learnt over the years which sps types appear hardier, others are really finicky. As I've gone really lazy, I now keep mainly the types that have stood with me through all sorts of mishaps.