A good rule of thumb is to get a skimmer rated for TWICE your tanks size. I'm using an eshopps 150 rated for a 150g tank on my 125g and I have to empty the cup at least every other day, sometimes sooner. I couldnt go with a reef octopus because of the space in my sump and a larger eshopps would have been too big. Better to have more than enough skimming than not enough.
180g Reef - 60g Rimless Reef -90G FOWLR- 125g Malawi Cichlids- 40b REEF- 34g Fresh Planted-working on- 20L FOWLR- working on
I have a mix of many different saltwater fish amongst my tanks, but I love my Tangs most of all.