If you were nearer to Vancouver, I'd loan him my UV unit, but alas, we are a couple of provinces apart. UV is designed for just this sort of problem & since it's only algae & not ick, you could use a faster flow rate & clear up the green water tout de suite. (pardon my French
) A Magnum HOT filter with a micro-filter/water polishing cartridge can function like a small diatom filter.
Good luck.
Anthony