I bought a dc10 for my Red Sea reefer 250. It’s rated up to 75 gallons (10 more than I need) and most important to me, it fits in the return section. I use my skimmer chamber as a fuge. I was planning to get an external skimmer before I found this one. It pulls good skimmate for me. I don’t use the top off system that comes with the reefer, I switched to a Neptune ATK. This let me raise the water level in the return section a little bit. I’m not sure it would work well without the slight increase in water level height. The slight fluctuation in water level doesn’t seem to prevent good functioning of the skimmer. I don’t think the water height fluctuates more than a 1/4” typically.