If you want to put some size on your pl*co, (and I'd suggest a bigger tank if you do), feed it canned spinach (no salt added). My pl*co has grown at least 2 inches eating this stuff - he loves it! I gave him a zuccini this evening, but he doesn't quite know what to do with it just yet (still looking for his spinach, I'm sure). The pl*co doesn't look at algae wafers the same anymore, though.
The only bad thing about spinach (canned) is that a cannister filter (or anything creating a moderate or above water flow) can make a mess out of it rather quickly - tends to clog intake on filters.