It would be simple multiplication, if the relationship is the same per volume of water. It may behave differently when immersed in a bath-tub full of RO, for instance (or not)...
And I guess new tank water, thanks.
If you need containers, I've been squirrelling away a couple... if my wife sees me use anything for the tank, she now sets it aside as "not fit for human use" - and it becomes fishroom property.
