Just use a turkey baster and gently blow the rock. Your hob will pick up the mess
As your tank is now you can get away without a skimmer. But once your bio-load increases you'll definitely want one. I went through the skimmerless stage, UGH! Lol-now I don't change yellow water any more or as often.
Whatever you do go slowly, and don't add to much. Because I guarantee your going to be wanting/needing a bigger tank!!!