Excellent! There is less chance of undesirable hitchhikers sheltering in the live rock when you select the precured live rock from your LFS, in the first place. If you have been taken the precured live rock and debugged it using both the club soda trick and a hypersaline bath, the chances are very good that you have driven any mobile pests (mantis shrimp, crabs, bristleworms or fireworms) out of the live rock before it was introduced to your aquarium.
To complete the debugging process, all you need to do is wait until your aquarium has cycled completely, and then introduce some peppermint shrimp and a small arrow crab or two for biological pest control. The peppermint shrimp (Lysmata wurdemanni) will chow down on any Aiptasia rock anemones that may have survived the cleansing process, while the small arrow crabs (Stenorhynchus seticornis) will feed on bristleworms and control any of these pests that may have made it that far. Between the two, and the debugging measures you’ve already applied to the precured live rock, you should have everything well under control.
Don’t worry about the pink encrustations on the live rock. That’s coralline algae and it’s very desirable on live rock. When conditions are favorable, the coralline algae will be spread over the live rock and cover it with a beautiful pinkish-purplish carpet. The colorful coralline algae is harmless to seahorses, very pleasing to the eye, and competes for nutrients with undesirable nuisance algae (hair algae, red slime algae, etc.), helping to keep it from getting a toehold in your tank. So you needn’t try to scrub off the pretty pink algae, sir; rather, you should encourage it to grow on your live rock. In short, the pink encrustations are desirable coralline algae and not the unwanted hydroids.
Seahorses often like to perch on live rock, particularly colorful pieces that are heavily overgrown with pinkish or purplish coralline algae. I always look for live rock that’s heavily encrusted with coralline algae for my tanks, so keep that in mind when you’re ready to add some more live rock. Aside from looking pretty, live rock also provides additional biological filtration (both nitrification and denitrification) for the aquarium and provides shelter and sight barriers that make the seahorses feel secure.
It’s a good idea to seed the live rock with copepods to help them rebuild a sizable population as quickly as possible.
Best of luck with your new seahorse setup!