26gl tank too small for 4-5" pleco??

I bought a common pleco about 4 months ago he was about 2-3" then and was definatley growing out of his 10 gl tank. recently i moved him into a 26 gl tank and he seems to be doing well, but i wonder how much more he will grow in this new tank and how long til he is too big for it?

Also he appears to have developed some light markings that look like stripes across his back. I know plecos change color sometimes but this has been going on for a while. could it be a health problem? please help!http://www.aquariacentral.com/forums/newthread.php?do=newthread&f=5#

thanks for the tip...maily i sak becaus large tanks are so expensive and i live in a very small apt with many other critters so space for a bigger tank is limited...but knowing me i'll probley break down someday soon and buy a bigger home for my "dragon"...thanks again