I have a 15 gallon water container you can have. I know space is an issue so I won't even offer you any of the 55 gallon drums I have... unless you want one.
How many gallons would you say is in the sump? 5 gallons a week is less than 10%. I'd up it to 20% a week for a while and I bet all your problems go away.
We need to get your rodi system up and running.
I know @under_water_ninja and @Arvin R both have personal tanks. As long as they are active members in the club and plan on continuing the chain i don't see why not.