What is this?
 

Can someone tell me what this is that's growing on my live rock? Is it good or should I remove it? Attachment 12740

Also have this other one. Attachment 12741

Second one is aiptasia , if that's the only one I'd rip that rock right out !!
Or you will be in for a mess

First one looks like a Manjo (no good). Second one looks like Aptasia (no good) kill them both!!!

How would you recommend I kill them? My lfs told me they were nothing to be concerned about so we left them and now they have multiplied real quick.

Yes both are real bad. Maybe inject with lime juice or cover in kalk paste

I have had great success in the past using Kalk paste. It is just 1 tsp. of calcium hydroxide to 2 tbsp. of tap water. I boil the mixture in the microwave before using a plastic syringe to feed the mixture to the anemones. If you get real close to the mouth without touching the tentacles and squirt a little bit they will suck it right into their body. Calcium Hydroxide can be had in bulk or bottled at the LFS. It may also be labeled as Kalkwasser by such companies as Seachem. You can also buy premade remedies such as Joe's Juice that will have the same effect. Peppermint shrimp will also usually prevent new anemones from occurring and are also a hardy and greedy little shrimp to have anyway. I would find a different LFS if I were you.

I have a syringe and needle with lemon juice.... I put the needle in the base and inject them with lemon juice until its comming from their mouth.. I do it every other day or so until they are dead.. not enough to alter the Ph in the tank...

If its on a easy to remove piece of LR, take it out and using a small needle/syrine inject the base with lemon juice. As they are tricky little boogers and will retract if it does this, just fill a small bucket of tank water and then submerge the rock until it comes back out, then stab it at the base.
~just be careful that you watch your water params as the lemon juice can dip some of your values. Then just do a small water change - no harm will come to your tank/livestock.

I found this to be the cheapest and easiest way to rid of the pests, can also try getting a peppermint shrimp to eat it (which may or may not work). I would lend you mine, but the last person to "borrow" it, has not returned him.

Just picked up some aptasia-x and a couple peppermint shrimp so hopefully that helps. If not I will be trying the lemon juice. Won't be asking anyone other than the experienced guys at pieces for advice anymore. Thanks for all the help everyone!