scrapping couldnt be ich??

[ortho]

hello all,
Ive 2 aquariums 55gal each. One is working perfectly(2 jags,2 oscars,2 convicts).The fishes seem all healthy and growing well.
The problem is with 2nd aquarium.it began 3-4 months ago.Ive noticed my malawi scrapping on the rocks but i coukdnt see any whithe spot on it.This phenomenon spread to all my other fishes in this aquarium.All are scrapping to the rocks from time to time .
But i cant see any white spot on any one of them!!
what else can it be other than withe spot?
All are active and eating well,but all are scarpping without exception!!!!!(i cant see any whithe spot!!!!)
can anyone give me some advice?
thanx.

[OrionGirl]

Could be fish lice--an external parasite. Check here: http://www.fishpalace.org/Disease.html , most the way down.

[Fisher Price]

Most fish do this from time to time so it is not necessarily a problem unless they are doing it continuously. If you do not see any other signs and the fish otherwise act healthy I would not worry about it.