weird cory behaviour

[elmj]

my corys have recently been seen 'sliding' on the gravel of my tank! :confused: i read somewhere that fishes will scratch themselves on the gravels if they have ich. so i check and inspected them carefully for ich. but they don;t seem to have it. is this a common behaviour or is it something is wrong?

edited: when i mean sliding mean they will swim and swim then suddenly for no reason they would topple over to their sides as thought they fell down and get up as quicky.

[NJ Devils Fan]

What are your water parameters?

[wetmanNY]

If they act as though their gills were itching, it's a sign that some ectoparasite is irritating their gills. Ichthyophthirius is one such. There are others.