This is the reason I add a ball valve to all my return pumps, just in case.
As far as the skimmer, what kind is it? Maybe you just need to adjust it, if you have more water in your tank it stands to reason you have less in the sump which may cause the skimmer to go a bit crazy
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.