What kind of algae eater? If its a Chinese algae eater 10g is way too small & they only eat algae as juveniles (as do most algae eaters) they will need other food as they get older. If you're seeing aggression already I'd say the tank already isn't big enough & its being territorial. This I know because I have 2 & they started out in a 10g with 3 female Bettas, now everyone is happily living in a 46g. The 5 fish I had in my 10g produced a lot of waste so if it were me I wouldn't do more than 5 fish total.