I am a degree-qualified scientist. I don't have 'blind faith' in anything.
As a scientist, testing is a vital tool in order to manage what one is doing. An alternative approach is to rely on experience but that only comes with the passage of time. The ability to combine both of these is the privilege of the few.
Well, in my opinion, your being a qualified scientist is a disadvantage, primarily because it seemingly imposes a degree of confirmation bias to your ideas. At least you do recognize that experience is a valid alternative, so that's encouraging.
Have a look at this article in venerable Krib:
Control of Algae in Planted Aquaria
The author of this article, Paul Sears was iconic in our hobby as he (along with Kevin Conlin) was responsible for the development of the PMDD dosing scheme. Now, Paul was a scientist, held a PhD in Organic Chemistry and had access to mass spectrometry, but he had a serious bias against PO4 and tried to limit PO4 as much as possible, so much so that PMDD does not contain any PO4. For years we continued to have problems when dosing PMDD, until Barr proved that PO4 is a vital component of nutrition and understands the laws governing plant health. Looking back at that article, it turns out, we now know, that almost every single assumption and conclusion in that article is wrong.
I've been growing plants for over 30 years and I've witnessed every single one of your arguments over that time - and - I've seen them disproven, not only in my own tanks, but in many other folks' tanks The reality of the test kits are that a sample made from distilled water , even if it is prepared stoichiometrically accurate, does not represent the dynamic behavior of those same compounds in the tank. It's the
behavior of the compounds in the tank and their interactions that falsify the readings.
Furthermore, no one gets into this hobby to test and measure things down to 0.01g or to fight algae. They get into the hobby to be aquatic gardeners, and no, testing is NOT really a requirement. One need not be a scientist to enjoy the hobby or to have success. But that isn't actually the problem in the hobby. The problem is that people are told that they
need to test in order to grow their plants. They are given false information and are frightened into buying these kits under the assumption that the kits can solve their problems. In this forum many beginners, and experienced alike, start their post with a long list of their tested water parameters, which are mostly meaningless and irrelevant to their problem at hand.
False doctrines litter the web and reliance on test results, once ingrained, erects a barrier to learning. THAT is the problem with test kits.
These would need to be investigated on an individual basis.
You're damned right it needs to be investigated. It's a pity that you haven't actually looked through the archives of this forum to see what works and what doesn't work, or paid attention to the degree of inaccuracy. Here, look at this poster child for test kit inaccuracy =>
ferts causing high nitrate!
This is just one example. There are plenty more. You just need to look and learn.
Cheers,