Well, if you try coming from the leaner side, you end up with hurting the plants.
If you come from the non limiting side(eg EI dosing), then reduce things down till you see a negative response as suggested above, then bump back up to the next highest rate, then you have healthier plants.
Also, combining sediment ferts with any water column dosing routine really can have dramatic improvements.
Test kits are slippery slope and few folks get into this hobby to test water.
Folks will often get into testing water for about 1-2 years or so, then get over that affliction and mellow out and realize that watching plants, good consistent care, water changes, cleaning filters, prune etc make a lot more difference in the end result.
I still test a great deal, just not for my tanks unless I have a more hypothetical question.
This tank for example has never been tested and dosed based on a test kit reading:
How?
Weekly 50-60% water changes, standard EI dosing, good CO2 and tweaking, routine pruning, no losses of fish(there's about 900-1000 or so in this tank) etc.
Amano likely does the same types of things and really ever suggest testing much if at all. The care he typically suggest is actually very similar to what I suggest, just leaner to the water column, but the ADA aqua soil makes up for that.
The other part, both Amano and I came to some similar conclusions quite independently.
As said also, you can vary the dosing via % easily, no test kit needed either.
You do not need ppms, you need to know how much to dose for that tank at the point and time(which can change!).
So you can later the dose without a test kit also.
Regards,
Tom Barr