UGH!! Stop it! /crying
Seriously, something totally went wrong here w/ all your tanks!! I'm beginning to suspect that the feeder tablets could have been the problem. But how?! They aren't suppose to kill fish like that and melt your plants! I really hope you find out what happened!
As far as the white spots on your Betta, I wouldn't be too concerned that it's Ich unless you start seeing him flash against objects. That was always the red-flag for me when my fishies had Ich. It looks to me like maybe they were caused by an injury, (rubbing against the driftwood, perhaps?). If you have any Melafix, that should help w/ the healing.
Again, I'm so sorry about all of your tanks, Daileene.
![Frown :( :(](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
I hope you find out what happened!
P.S. There's one last thread of yours that I haven't checked yet, but I can guess what kind of update you have for us.