Iv been in the hobby for a little over 2 years now and never thought to ask the question until now. I have upgraded from a Innovative Marine Nuvo 38 to a 50 gallon with sump. In my old tank I had a little protein skimmer where it didn't really matter and now I have a huge one that I'm in the process of breaking in. Now on to the question when my skimmer is taking a lot of water and putting into the cup to the point I need to top off what water should I use salt or DI. Does the skimmer remove any salt from the water? I know it takes poop and what not out but I just wanted to ask. I hope the questions sounds right to where you all can understand.