I have a little skimmer that was rated for up to 100 gal , my tank is 80 gal. I had issues with it on and off but it cleans the water at least it had a lot of green gunk in it . I had a lager octpus reef skimmer . this this is big . just barely fits in my sump. I not sure how big a tank it will do but I am sure it is well over 100 gal. It is a older model I have had it in my shed for a while. It is working but the gunk in it is not as dark as the little one , is this normal ?