Tiny White Worms

[guppy]

Just as a point of information, if the white worms are flat and tend to stay on the glass they are almost certainly planaria, interesting little critters. With a good magnifying glass you can see that they have an arrow shaped head and two eyespots.
If they are free swimming and round bodied they are probably a variety of round worm called a microworm.
Both types are good food for small fish and are sometimes grown in cultures as fry food.
They are harmless. As others have said they turn up in almost all established tanks but you seldom see them unless the tank is over fed, careful feeding and regular gravel vacs and rinsings of the filter pads will get rid of most of them as well as help with the gray water bloom.

 

[fishnutham]

they really tend to be a large problem in oscar tanks because of the messy nature of the o lots of excess food get trapped in the filter and you will find the majority of the colonys there rinse your filter media out in old tank water often and try to feed a less messy food i cut back on the pellets and feed more frozen smelts and krill of course his pellets are soaked in vitamines and garlic to provide him with a good balance