[unclejed]

1. yes you can leave them in.
2. Rinsing in the removed tank water, scrub, dunk, scrub, you know, until it looks real clean.
3. The pre-mix is great and no you don't have to change it out.
4. Now as for the aptasia, as far as the remaining rock in the tank, how many aptasia (estimated) would there be? if less than say 10 use Joe's juice. I am not familiar with what you are using. Joe's juice absolutely kills them instantly. So injecting 10 would be a little work but not too bad. Also, look into buying a Porcelain Shrimp, I have used one, they love aptasia.
5. if you could buy a multi-media reactor ($40.00) and run Phos lock or other suitable media you have for removing phosphate that will help a lot, if not, do the things you said and do 30% water changes once a week for 2-3 weeks to get things under controll. Don't scrub the rock. Hopefully it will die off. Also, add about 12-15 more blue leg crabs to help out, you will see a world of difference.