Why water change day seems to grow aquatic plants better

[Solcielo lawrencia]

If I just refill with the water I took out, how would fertilizer dosing be affected? I couldn't just dose as I normally would.

[Tom Barr]

If I just refill with the water I took out, how would fertilizer dosing be affected? I couldn't just dose as I normally would.

Well, you'd not dose because you are isolating and only testing the water pressure.
Same if you had a potted plant and wanted to raise it up for a few minutes, then return it.

You need to account for the increase in lighting for that few minutes, but otherwise, that's a fairly easy method I would think.