will a bristlenose pleco eat plants in a planted tank?

Have two of them, no problems with plant eating, I don't even give them special food, and they don't bother when I feed the other inmates. In the 5 month I have them, they have grown quite a bit, about 50% more than when I bought them.
I might be wrong, but should I give them special food if there are enough algae? Please advise.
 
They should be given veggies, too. Mine gets a slice of zucchini a few times a week, and some shrimp pellets.
 
I have a dozen juvies in my 55 planted and they don't touch my plants.
 
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