I love newt!
I think you do not need to scrub, that will take all the balance out of whack and the pond will have to be cycle again.
I'd just reduce the water until it's almost empty, scoop out the muck algae as much as possible (while looking for any critters and move them to a safe place), use sodium percarbonate on the algae (leave on for 20+ minutes) then put water back in the pond again, then wait a few hours and then drain the pond again. Or even use the sodium percarbonate on the muck, it'll make the muck float and you can skim them out of the pond. I do that in my pond and the algae will slowly die and disappear in a few days. Then I do a bit of water change again to reduce the ammonia the dead algae caused.