Originally Posted by ray-the-pilot
So if you do 4 x 20% water changes the resulting dilution is:
(1-.2)^4 = .4096
Which is better than 1 x 50% water change
(1-.5)^1 = .5
So ~40% dilution .......and that is somehow MORE than 50%?
That's not clear.
PMDD addressed this over 15 years ago:
Near the bottom.
Better than this, let's just use a modeling calculator:
Doing a water changes takes roughly the same time to drag stuff out either way, so if you go to the trouble, might as well go big. That's a fairly obvious practical matter. So you end up doing 4X more labor for less effect at mitigation of any build up.
Seems silly to waste one's time/motivation going small.
You can run the graphing function with 50% once a month and then 20% weekly and then look at the assumed uptake ranges over a few weeks.
With Reefs and the cost of salt mix, this is a larger economic factor, but of little consequence with Freshwater. Still, Reefs/marine systems benefit from large water changes very well.