Our toilet valve refills as we get evaporation. We drain the barrels
and the berm ponds annually to dump the muck form the pond. That does
actually mean turning over 1000 of 4000 gakllons. That is an annual 25%
change over...staged. We have monitored the water chemistry and it does
not seem affected by the low change rate. My observation is that the
pond does a good bit of topping up, which should be concentrating the
minerals.

Jim

Is this a water garden w/koi?

Your last sentence confuses me, as the reason it is recommended 10%/week is
to keep heavy minerals, pheromones and other pollutants (that most
hobbyists can't test for) diluted and to add necessary minerals, vital for
the fish.

If a koi only pond, they usually need to do them for the nitrate build up
also.... something we rarely have to worry about in a water garden plus
koi. ~ jan