My pleco has some wierd stringy white stuff on him
Anymore details? No changes in tank?
Is he otherwise healthy and normal. Does he hide away a lot or have you done a water change colder than normal lately?
If he is still rushing about normally at feeding time I'd suspect fungal. One of mine hides away a lot and will pick it up. Perhaps he scrapes getting into a hidey hole and then tends to sit there egg guarding maybe in an area of poor water flow.