if I got one would I have to buy them a special food?
If you have algae in your tank they will eat that as they are great algae eaters. Algae wafers or veggie rounds are a good food for them when there is no algae to eat.
Until they get the walls of the aquarium and the decorations and the floor cleared of the tiny little bits of algae, I would not feed them extra food and when they quit starting to fly all over looking for food that means they have pretty well cleared all the algae. Then you buy them either veggie rounds or algae wafers and feed them a small amount depending on how many you have every other day or so. I give my 2 about a half every other day and if they do not have it eaten then they have to wait another day until they eat it. The tank I have 3 in gets a bit more than a half wafer but the same rule applies, if they do not eat it in a couple of days, they do not get another until it is eaten. The only way I remove it is if they leave it until it starts to grow.
They are really good at cleaning the algae if you do not start feeding them commercial food too soon.