Maybe you just need to stop spraying them with water every six minutes... But sounds like you already have stopped? If you water them just slightly less so the top layer of soil isn't so wet, that might go a long way to stopping the algae.
UV light will help kill algea as well. If you can expose the pots to some unfiltered full sun outside for a long enough time...But then of course you would need to worry about shocking the sarr seedlings as well, so you would need to do it slowly, perhaps. But maybe that would defeat the controled aspect of your experiment...? And now I'm just blabbing random ideas.
Springtails have also helped a fair amount in some of my pots, as was mentioned; but my pings and small dews have taken a lot of them out. lol