| mmmm, that's an interesting question
A 'water change' is typically a removal of a set amount of water ( let's say 50% to make the math easier) and then the replacement with pure freshwater. So there you have a dilution factor of 1/2.
A 'top off water change' of course is not the same. The older printed literature cautions newbies to not conside this a water change at all as you are not diluting anything. That is true to a degree but it is not a useless endeavor. A top off adds back both buffering capacity and mineral content, it just doesn't cut pollutants that are already produced.
What you are doing is perhaps the most meaningful water change, that is a targeted water change where the most polluted area of the pond system is removed. The dumping of the sump, for instance, and an addition of new water is very effective as you are loosing both organics and the 'future ammonia' and ultimately the nitrate that ammonia will produce once the heterotrophic species get to it .
And since one of the byproducts of organic oxidation/reduction is DOCs, you have a very targeted water change when you remove waste from filters and free up the biofilm of excess organic build up ( a heterotrophic bacteria feeding ground).
So I'd expect that you will see less DOC on the surface. However, what is already in circulation will be very much attracted to the surface and you might have to be patient and do the routine for a while before you see results. - JR |