Since you're starting all the way over from scratch, I wouldn't use none of the old water. The peroxide will do the trick by getting rid if all that say on the rocks, just let then sit in the 50/50 solution for about 5 mins, and then you'll start to see the rocks start to fizz, and algae will start dying instantly. Hot water and vinegar will make your tank spotless again. You'll have to go thru another cycle which could take a few weeks, but I'll give you a piece of live rock out my system to jump start it. I'm not sure about the epoxy. Good luck bro.