Do you spike your PMDD after a large water change?


Boring background follows:

I've been adding about 2 ml a day of PMDD to my Plant tank (75 G -eventually
community tank) for 6 months. I add N separately, so this is not part of the
mix. It tested at .1 FE a few months ago, but I have not tested it since, as
everyone looks happy.

I rarely did water changes in the beginning as the tank did not have any
fish. Although I've been doing weekly water transfers between the Plant Tank
amd the GF tank to give the plants some nitrates and the GF some fresh water
(besides their weekly cleaing). I tested the FE today and it was about .25,
despite the increased water changes? I guess I'm overdoing the PMDD?