Bacterial scum in blackworm tank

[Axodragon]

I raise blackworms to feed my newt & axolotls. Lately I've been having a terrible time keeping the worms alive, and some sort of bacterial scum seems to be the cause. No matter how often I change their water, it's immediately dirty again (slimy, foul, and looks like sewer water).

I'm worried because my worm population is declining rapidly, and I don't have a way to buy more in a hurry. I don't want my amphibians to go hungry!

I was wondering if anyone else has had problems with this, and what I can do to fix it?

 

[Twylenn]

Have you found a solution?