So I've decided to start a challenging beginner saltwater aquarium in a 10 gallon nano reef. I've created a pretty slick wood air stone nano sized protein skimmer using some PVC for almost next to nothing and I'm very pleased with the outcome. One question arises though. How much above the water line should the skimmers opening to the catch cup overflow sit? It's working good right now but bubbles are only being produced very low into the tube is that just because it's an empty tank with literally nothing but the mixed water ?