Iinitially it was never meant to be a method per se. Just a re set.
You can go 2-4 weeks without a change. But you need to work on getting to know the tank and the plants better.
That takes time.
When you see a lull of a trace of algae, you respond by pruning, trimming etc and do the water change and re set.
I've always suggested to start with an assumed max rate.
From there you can lower a nutrient one at a time step wise.
When you see a negative plant response, bump the dosing back up one notch. That's the minmum nutrient demand(MND).
You can figure out each nutrient this way, CO2 and light also.
What you do nopt know is the max amount before we see negative repsonses.
I know 120ppm of NO3 is bad, for shrimp and plants.
I have no clue nor would I think anyone would add more than that or more than 10mls of Flourish in a 4 gal tank daily, 5-10ppm of PO4, 100ppm K+, GH over 450ppm(25 degrees) etc.
Non CO2 tanks should work from the minimum prespective.
Leave the max experimenting to the CO2 folks.
Weekly doses work well for non CO2.
Every 2-3 days for the CO2.
This gets into a number of issues...........frequency as well as amount dosed.
But in each case..............you still can do a great deal of experimenting without using a test kit and these test will more accurate since there is no test claibration involved or related error.
Your "test" as were, ARE the plants.
I think wasting traces, having to do more water changes than some care to are the main issues and also...........some people like to play with test kits and feel like it's more scientific somehow in their approach.
They might not want to fess, but they do.
If you seek balance and reduced water changes, go non CO2.
If you seek more growth, and some water changes, go CO2.
You do not get both, although some like to think they somehow should be able to. They want an Amano tank with no work.
Amano work's his tail off to get the tanks in good shape.
He also does large water changes, adds MND, adds his ferts frequently.
I've done some truly beautiful non CO2 tanks. They are really neat and nicer than my CO2 tanks on any given day.
But I also estimate the dosing on those and seem to hit things well, I can simply not dose for a few weeks to pruge the tank of nutrient build up.
That's why it's good to have a little less than your nutrients needs coming from the fish.