Worm-like Parasites

I have white worm like parasites swimming around my tank and in my rocks in both of my Oscar tanks but not in my community tank or any of my Dempsey tanks. I did a water change on both today and yesterday but they are still floating around and in the rocks. What should I do and are they harmful?

 

Pictures would help.
How long has the tank been set up?

 

I tried to get a picture but there way too small. There white and stringy and you can see them squirm around. The one tank has been set up for about 9 months now and the other one has been set up for a month.

 

It sounds like detrius, but I can't really tell without a photo. Are they on the glass too? How big are they?

 

There about half a centimeter long. There in the rocks and up against the glass but only where the rocks are. They come out when I gravel vac and some get sucked into the filter. Others go back into the rocks. I had algae problems with the one tank that has it the worst and just fixed that problem after 3 weeks of fast growing algae. Don’t know if that could help to identify. I’m still trying to get a good picture but it’s hard to because of the size.

 

Most likely detritus. They're harmless. I'd vacuum the substrate really well for the next week or so.