They will only eat plants if they are not fed. I go out of town for a month at a time sometimes, and my 11 year old daughter sometimes goes days without feeding them, and that's when they go after the plants a little. When I am home, and they are fed regularly, they don't touch the plants, except to eat the dead leaves that fall to the bottom. They are great for planted tanks otherwise. They keep all surfaces on the tank spotless, and take care of any leftover fish food. They'll even take care of any dead fish that rest on the bottom.