Plecos will grow to their surrondings, but it is very unhealthy and basicly you are stunting their growth.

I have an 11" pleco living in a 75 gallon tank at my uncle's house.

A ten gallon is way to small for even one regular sized pleco.

This site will give you an idea of how big your pleco will get:

http://www.liveaquaria.com/product/s...cfm?pCatId=837

I beleive the tank requirements and size are to the right.

Are the ones you have greenish brown? Those are the ones most commonly sold, and those will get around 11".