The point being removing water and replacing it a 20% every week or month does not reduce toxins only to a small degree.
I presume you meant that it
does reduce toxins only to a small degree.?
Yes, by exactly 20%.
Work up a spreadsheet and factor what a water change of 20% water or another value works out to.
Yes, I've done that extensively and published the results. It was linked in the third post of this thread. Did you check it out?
Here's a graph from it that is relevant for anything that is not also being continually added. You can clearly see that an impurity is dropped substantially.
Figure 1. Nitrate concentration as a function of time when performing water changes of 0% (no changes), 7.5%, 15% and 30% of the total volume each month. In this example, nitrate is present at 100 ppm at the start, and is not added or depleted during the course of the year except via the water changes. The y-axis can alternatively be thought of as the percent of the original concentration remaining for any material that is not being added or depleted from the water except via the water change.
and this one shows what happens generally with something that is being added continually, as from foods, supplements, CaCO3 reactor inputs, etc. I used nitrate as an example, but the concentration of anything that starts high and is slowly added applies equally well:
:
Figure 3. Nitrate concentration as a function of time when performing water changes of 0% (no changes), 7.5%, 15% and 30% of the total volume each month. In this example, nitrate is present at 100 ppm at the start, and is accumulated at a rate of 0.1 ppm per day when no water is changed.