I used to have the brown kind on my rocks covering everything. Every so often I'd scrape them off but they go deep into the rocks so it's difficult to control that way. You can try covering/smothering them in epoxy (you can always remove the epoxy later).
Mine started to disappear after I got a potter's angel. I have read somewhere that pygmy angels can sometimes eat them, although I never saw it happen - but something caused them to disappear. So, if a pygmy (dwarf) angel is something you wanted and can fit in your tank and you've just been waiting for the right excuse to get one - here you go.
