Gold Spot Pleco

I have a friend who is dismantling a tank and wants to give me his gold
spot pleco, about 4 inches long.  I have a 55 gal well planted tank with
algae on the back and side walls.  My nitrates measure zero.  If I add this
pleco, will he chow down on the plants, or will he be content with the
algae, and algae wafers when the algae on the glass runs out?  My other
question is, as long as my nitrates measure zero, is it all right to add
another fish?  I don't want to overload the tank, but since I don't have
any measurable nitrates, it wouldn't hurt to add him, would it?  Is there
anything else I should be considering?  
"Candle?  What candle?  I don't see any candle, it's too damn dark in here!"