Thank you, it is good to hear... so I don't need to rush and buy some surgical tools to remove them one by one... All my rock system is one solid rock with a lot of caves and cavities...Most likely hydroids. No need to do anything special- they will go away on their own in time. They are very common in young tanks and will initially rapidly grow in population.
It is too far for me to seahorses...Manual removal of hydroids is nearly impossible. I wouldn't do a thing. I haven't seen any reports of harm to coral or fish. They are a concern if you had seahorses or some other very special animals, but for your average mixed reef tank, they are often part of the maturation process.