This is not sounding good.
First, fish in store tanks rarely if ever behave "normally." They are likely under stress from inappropriate water conditions, overcrowding, whatever. Bring a fish home and put it in a more suitable environment and it will behave as nature programmed it; sometimes quickly, sometimes over time. But thousands of years of selective evolution are part of the fish's physiology and it is not going to change.
Algae and algae eating fish. First, do you have algae? If yes, what type? Most of the problem algae in tanks will not be eaten by fish with a very few exceptions.
One should never buy any fish to solve a problem. Fix the problem. The possible detriment to the fish, or the other fish, or the aquarium is not worth the risk. I have fish that eat common green algae in three of my tanks, because I like them as fish. Rineloricaria parva
, Farlowella vitatta and Otocinclus macrospilus
. Considering how they all appear when the meal gong is sounded, there can't be much "algae" in the tanks or they wouldn't be hungry for sinking foods.