What about a non CO2 plant tank though?
E.g. no water changes for months/years?

You can still remove the chemicals with Activated carbon in such tanks also :idea:

By default, the non CO2 approach does not test the water parameters seldom if ever. That's part of the allure and simplicity.

What I did some years ago, was this:

Observation: some plants did poor in the the non CO2 tank. Some did well.
Over time things ebbed and flowed, some plants wasted, some flourished.

I removed the soil and dosed just inorganic ferts with plain sand/flourite.
I found that fish food left you a deficit of K+, Ca, Mg, SO4(likely), often times NO3 and PO4. Traces are often added to non CO2 tanks so those where not tested nor would doing so reveal any new insight due to testing issues for Fe.

Fish waste added a fair amount of N and P, but often once the plants grew in, these where very low and consumed rapidly by hungery plants.

Adding KNO3 and KH2PO4 enhanced growth.

Not all aquarist have the same fish loads either.
Adding trhe GH booster really helped things, once a week of these was enough to allow you to grow most plants, up from 50 species to about 200 with these routines.

With the test kits, I found a fairly robust range that was about 7-12 x slower than the CO2 enriched 3-4w/gal tanks.

Most of the problems folks assoicate with plants in non CO2 tanks are not allelopathic, rather, limitation based.

You can be an arm chair philosopher and speculate till the cows come home, offer research support etc, but unless you test and see if something works or not, you will not gain much new insight.

From such test and questions, we learn a lot more than from speculation.
We often specyulate to hopefully answer the question/s in the future and have some one new come along and advance what is known about a subject.

Raising good questions is also a great idea.
She certainly did this more than any other IMO.

Regards,
Tom Barr