Problem with Watermeal

I have a 25 gallon tank that is infested with watermeal. Several times a day I use a cup to strain off every floating piece I see, which counts in the hundreds. I get nearly all of it, everything seems fine, I leave for a few hours and come back and there are literally hundreds more at the top. I've been doing this for days now, several times a day.

Is the water filled with microscopic watermill seeds or something that grow and float to the top while I'm away? I don't understand where all of this is coming from. Is physically removing this stuff from an aquarium impossible?