disaster strikes!!

[sharelove]

Here's what's happened/happening: Last Friday I was mixing my change water as I do every week (I then let the salt mix and a powerhead do it's thing until monday when I siphon/add the new mix) and this is one of the things I did different: I added Kent's superbuffer straight to this mix instead of first dissolving it in fresh water as the instructions say. I forgot...when I added it on Monday, it was still cloudy. Just before the water change I had done all my tests, everything was in order. Alk was a bit low at 2.7. I received three new fish the week before: flame angel and 2 bangaiis. I acclimated and used paraguard for about 45 minutes everyone was happy put them in. For the first 4-5 days, no probs everyones eating happy curious -especially the flame. Then after the water change everything within the next 48 hours becomes a nightmare. First the flame stops being curious and isn't eating 24 hours later: dead. within 12 hours of that, one of the bangaiis dead. 12 hours after that the other one dies. My kole tang, my biggest fish starts looking greyish everywhere sunken around the eyes loosing color very fast and hanging out near the top as if he/she wants to leave. Open sores start appearing, especially two horizontal lacerations near the tail. Dead 24 hours later. My royal gramma stops eating 12 hours after that. Dead this morning. Of my two clown percs, one is newer than the other and bigger appearing very normal and healthy last night, dead this morning. the only fish I have left are all the original ones I first started with 5 months ago: the smaller clown, a neon goby and 6 green chromis. All my inverts seem to be fine.
What in the devil is going on???? I took an alk reading on thursday and it was a lot higher: 5.8 and I had just added purple up on the monday after the water change. I have 4 corals and a friend gave me the PHyto Feast and that's been newly introduced. I can't think of anything else that's different.
Please help.... sniff sniff sniff...