EI just eliminates part of the issue.
Same with most fert routines if you follow them.
The other parts are CO2 and light.
There's a 4th part as well.
Rather obvious, but very often over looked.
Basic aquarium mainteance, things like cleaning the filter, water changes, cleaning glass, running a diatom filter if there's algae or muck in the water after you redo something or do a large change. Good current, adequate filtration, wise fish loads, good algae eating crew..........
Basic stuff, but I do not k now how many times folks have claimed they are doing everything right, then I go over to their home and there's virtually no filtration, tubes are clogged, media has not been cleaned of changed in months etc.
and they say it's my fault that EI does not work for them
You need to be careful in ascribing what/who to blame when it comes to algae, the tank, etc.
It's not a single variable system.
I have no idea why so many assume it is.
There's no one silver bullet.
Older folks that have experience know this, but the folks with a little knowledge to be dangerous, but not enough to put it all together are often the problem.
They think they figured it out and cannot see all the parts yet.
So they claim false evidence and draw poor conclusions.
I mentioned the errors in the logic, they think they are right, so poo poo me, it's easier than admitting bad logic(at least to one's ego, not in solving the issue).
If I had nickel for every time that one happened I'd be rich
When you approach these questions, think about how you could reduce things down and isolate one variable. Providing non limiting nutrients will rule, them out.
Well you can use commonly used real low light and real high light and then some in between. That will cover most of the tanks folks deal with.
Measure with a light meter is useful, but not needed. Light, unlike nutrients and CO2, is very stable over the 3-8 week test periods typically.
So you can assume it's stable.
That leaves our good friend, CO2.
You will see me moving more and more towards it over the years as a primary test focus.
Along the way, I've found some new ideas and methods.
Much more than we knew prior.
And there's still yet more to come.