New problem or maybe not. On the water feature I have black worms 'growing'. At first I thought they were blood worms but it is as if they have pods that they come out of - also on the water feature. Many thousands. After I accidentally killed almost all of my Koi by accident over-dosing them on Connie's Crystals these worms disappeared for a while but now they are back. Does someone know what it can be. The are 3-5mm long.

Have you got a photo?

I think it's mozzi larvae...had the same on my waterfall

I have a pic but its such a mission posting it. If they are mozzi larvae, I'd be so relieved man. Will post the pic later. However, they were there in winter time as well.

I've got them too. I think they might be leeches though? Will try and post a pic