i agree that its very possible. after all the fuge is a filter and with any filter if you remove it from the system of course it cant do its job anymore and anything that it was filtering is now going to be free to increase within the tank, especially if there is a steady producer, regardless of what that might be. think of it this way. if your pouring salt into a bucket over your tank your salinity isnt going to increase but if you mvoe the bucket (the filter) then as the salt starts to increase in the tank because its not being filtered out anymore then your sg levels will increase. i think this is what happened with your fuge. you took your major nitrate consumer out of the loop so the nitrate begain to build. i agree with whoyah, take the fuge back offline to test in more controlled conditions.