I cleaned some of the mineralisation off the moss as people here suggested and afterwards noticed these guys! I think it’s a nematode giving a piggyback ride to a springtail? I haven’t deliberately put them in there, I’m thinking they probably came with the moss which I collected from a path at work. Or maybe from my rainwater tank? Either way, it’s looking great now so I also wanted to say thanks for the advice!
by pelka-333