when does a water change become irrelevant

[Proteus]

So in the last month I've launched zeo and tm balling. Switching from prodibio to zeo I had a po4 increase but thanks to the people at the zeo forum I'm down to. 08 and dropping.
With zeo and tm balling I should have zero nutrients and water should be topped up on the big three plus trace.

So what's the point of a water change at this point? I haven't stopped my routine only slowed it down from 10g a week to 5g