Looks like whatever it is has already damaged new growth

Any tips on removing them? I’ve been spraying them with SB plant invigorator in recent weeks but only just noticed this

Thank you! I feel very welcome

Hi I’m Trev, a new member of the Macclesfield and east Cheshire branch. Only been collecting for a couple of years but pretty much obsessed. Currently limited to a couple of sunny windowsills but already planning a larger space outside. My wish list cactus that so far seems to be very elusive is a s...