if you add one, please, please, keep an eye on it. i have heard that they will suck the slime off of the side of our discus'. especially at night while they are sleeping. if you have observed your discus sleeping it can be scarey, they sleep on their sides and almost have a dead look to them making it easy for the pleco or algea eater to suck them. my husband just put one in my discus tank, its yellow, i am all over it. so far no strange marks on the discus, but he better watch out. i am watching!!!!