supamarine - I'm not familiar with using a canister filter to do a water change. I still think the new water should be mixed with salt and circulated, at least 24 hours prior to being introduced to the tank. So, the new water would be in a separate container and get pumped into the tank after the old water has been pumped out. Sorry I couldn't be more helpful...hopefully, someone else can give you better insight with the canister filter.