pic #3 is also hydroids, colonial.

Collonista snails are generally considered harmless and reef friendly and are helpful in controlling algae but as you have found out tend to breed like rabbits I lucked out in that my Yellowtail damsel developed a liking for them and only them as I haven't seen any in quite some time.

There are wrasse that will eat them but then they may make meals out of your other snails, crab and shrimp as well. From what I have heard the best way is the old reach in the tank and pick them out with the fingers routine.

the collonista snails are good. Eat algae, uneaten food and detrius
Keep them,

I had an out break of the a few years back......and tried several things to get rid of them, nothing worked. I had a bunch on the rubble in my sump, I even went as far as to take it out and let it dry in the sun for a few weeks.....upon putting it back in POOF they were back again.

Eventually they went away on there own, and to this day I never noticed any ill effects from it being my tank.

As for the GSP I wouldn't worry about it, that stuff is indestructible.....in fact there will prolly come a day when you'll be swearing trying to kill some of it back LOL

I have taken the rock with the hydroids out of the tank and blasted just that part with a propane torch. Worked for me. Wear protective eye wear.

thanks for all the ideas everyone. This has been most helpful!

L

so I have noticed that the snails are plateauing at a steady pace so not too worried about them any more, however those dendrite hydronises things or whatever are getting numerous, any suggestions?