I realize that one will have a faster rate than the other. My point is
it doesn't matter because they all are moving in the same direction, just
with different rates.

If the consumption of certain ions is slower than the replenishment
rate than you could keep up with water changes...

Lets look at it again:

"Water changes of approximately 10 to 25% monthly help to limit the
long-term change in the ionic composition of seawater in a closed system
aquarium."

The water changes help to LIMIT not PREVENT changes in ionic composition.
Why are you having a problem with this?

"Limit" could mean anything. It could be limit by 1%, 2%, 3%. We don't
know do we?


They also only say "limit". How much is it limited by?
It could be only 2-5%.

Or 80% - it will depend on the rate of the water change
and the amount of consumption of ions by your corals...

I really doubt it's as high as 80%.


Oh, right - you do not have corals! :-)))
What do you do in the *reef* forum than ?

To help you people. Especially YOU.