New tank needed?

[Raeka]

My pleco is likely a Pterygoplichthys pardalis or disjunctivus or a hybrid of the two. We've had him for about 6 years and when we got him he was only a few inches long and what we read about common plecos put us under the impression that he would only grow as large as the tank so we thought we were doing ok with him in a 45 gallon hexagonal tank. We're moving and its only him and a ghost shrimp now so we were looking at getting an even smaller tank. He's about 6-7 inches long though he looks perfectly normal as far as we can tell but the descriptions for his likely species say he should be in the teens lengthwise. Water parameters that were measured using a test kit were always in what seemed a normal range i.e. no ammonia, no nitrites, nitrates at about 20-30 ppm, a pH of about 7.8 and a temperature of about 75-78°F. He has been fed algae wafers and other bottom feeder pellets and flakes along with the occasional zucchini slice. He has 3 pieces of driftwood, a cave and many plants.
My questions are:
a) is he likely stunted even though his environment has always seemed fine and not overloaded?
b) if we move him to a bigger tank at this point would he likely grow anymore?
c) if he should still grow how much more growing is he likely to do and thus what size tank should we be looking at if it stays just him and the ghost shrimp? d) I read a few places that pleco growth/stunting has more to do with nitrates than space, what are people's thoughts on that?

[Barbie]

He will continue to grow. If the water parameters are not too foul, the probable limiting factor would be more readily attributed to lack of food, IME. These fish eat a pretty large amount of food and are rarely adequately fed in aquaria that is not geared specifically to them. Clean water, enough food, and enough space to turn around and you will see quite a bit more growth out of him.

Barbie

[Raeka]

What would be considered a good amount/kind of food for him?