Almost assuredly, your UV sterilizer is what is preventing you from
being able to grow algae. I have plecos myself (3) and I feed them
Hikari Algae Wafers as usually my tank is algae free (though currently
I am battling an outbreak of Staghorn algae). They love the wafers.
I've also heard of people using blanched zuchinni to feed their plecos.
I don't think you need to grow Algae unless that's just what you want
to do. If so, turn off the UV sterilizer and you should begin seeing
some results soon depending on the normal conditions of your tank minus
the UV hardware.