|My Bristlenose Pleco "Eval"|
My bristlenose pleco (whom I have had for several years now) seems to love TetraVeggie algae wafers. I've had guppies and goldfish also nibble away on this. I usually drop in half a wafer in my tank every other day (not daily because I still want my pleco to keep any possible algae growth obsolete).
To prepare cucumber I start by washing the cucumber off in hot water (you can go the organic route if you prefer to be on the safe side), peel off the outer skin (as the skin tends to go uneaten), slice the cucumber in 1/2in thick cuts (or you can slice it long ways) and try to pick off any seeds, and then soak the cucumber in a container of water in the fridge for several hours (this helps the cucumber slice sink to the bottom). A single slice can generally feed a bristlenose for a good week (although you may want to remove the slice after several hours as to not pollute the tank).
Brown and Green Algae
This generally occurs naturally in an aquarium with too much lighting (the reason I bought my pleco to begin with) and my pleco is always in search of this as she is consistently cleaning (and she does a great job of keeping the algae at bay).
Side Notes: Among other things I have read people feed bristlenose frozen bloodworms, but I have never seen her eat that or show any interest in them. I also find not all algae wafers seem to interest algae bottom feeders. Some say bristlenose need driftwood in the tank to help their digestive system and provide them with more fiber in their diet, but I have not found it to be necessary... although they do seem to like having adequate dark hiding places (caves, pots, etc) and I believe this is because they generally breed in dark areas. My bristlenose does get a little territorial over her wafer until she has had her fill to eat (she kind of darts at other fish to chase them off her food.. nothing that causes any real harm though).