I should be picking up a 145G tank that I will be using as my display tank, shortly after that I will be getting a 75G sump/refuge tank. The skimmer will be in the sump tank. I know that skimmers are rated by volume, and I should get a skimmer with a higher rating.
Question is, do I get a skimmer rated for the 145G tank, the 75G tank (since that is where it will be) or do I get one rated for total volume of the whole setup?