Some assumptions often are discussed about dosing methods, EI is no different.
One of the main criticisms are water changes. Many hate doing them. Newbies are particularly easy to manipulate with such advice suggesting no or very little water changes.
The old fish breeder? Not so much, they know better.
Still, this does not address the facts about what is the best management approach.
You can modify EI in a very simple way, without a "test kit".
How? Start with normal EI dosing and then slowly and progressively reduce the dosing rate till you note a negative plant growth response.
Then simply bump back up to the last prior dosing level. This is the ideal dosing rate for your tank. This takes a few weeks of reduction to do it correctly and of course watching your plants and growth, but you will do this anyway.
Unlike lean methods, this approach does not stress the plant's full potential of growth, it targets what is called the "critical point".
EI is somewhere about 1/4 the way past the Critical point for most aquariums, maybe a very high light tank might have a critical point of normal EI dosing.
But virtually all other tanks will have a lower critical point.
While you can keep doing EI and large water changes, there's no harm, some aquarist feel weird about it. Large water changes and more the better help planted tanks, few will argue that. Still, they get squirrely about dosing more ferts than they need.
While this does no harm, there's also no need to lard on more ferts than are needed.
If the goal is reduced water change % and/or frequency, then targeting this critical point is a key point.
It's not that hard to do either.
I should point out that lowering your light intensity will also reduce the work and water change frequency, thus slowing everything down in the planted aquarium also. This makes everything much easier to manage and keep on top of, including reducing.
I change the water monthly on this tank:
the water change frequency and amount.
Plant biomass is much lower than many other tanks, so I dose about 1/3 EI. This is a VERY easy tank to care for.
Once a month water change. No trimming really, I'll cut a sod piece and sell it once every 2 to 3 months but that's about all.
So the aquariums can look very nice and easy to care for using this reduced water change method.
If you start with ultra lean dosing, then you never see what nice full growth looks like.
If you want to see this, you need to have good CO2 and light.
If you need to test CO2 and or light, you need a method to make sure there is no dependencies on nutrients, EI is the best and frankly the only method that suggest that approach.
Leaner methods end up stunting or slowing growth and you never know what the good growth independent of nutrients even looks like, this is bad for a hobbyist interested in growing plants well.
So you can use EI initially with water changes, then reduce the dosing down to the Critical point, then reduce the water changes, say 50% every 2 weeks, observe.........
Then 50% every 4 week and observe.
One water change a month is good safety net for most aquarist.
You can certainly go longer, but good management that's proactive starts to get dicy beyond this.
Many wing it and things are fine, others end up with issues.
Still, dosing is a small factor in all of this and the success, most of the issues folks have are CO2 related or they have too much light for their management goal.
If you want less work and less water changes, then low light is the best place to start, that will provide the most wiggle room for CO2 and for dosing ferts.
Lastly, if you do like to avoid water changes, then sediment based rich ferts will work well in your favor, eg: soil or ADA aqua soil works very well and provides a back up if you run too lean. In the initial stages, these products will be rich in NH4, but after 6-12 months, this source will be exhausted. So make sure to increase the KNO3 dosing a bit as time progresses if you want to keep the same rates of growth and plant health. I use them and suggest other hobbyists use them also as a good back up never hurts.
New tanks= plan on doing 2-3x a week water changes(50-90) for the 1st 1-2 months.
Then trim the dosing/water changes down and observe.
Got a problem? Go back to water changes and richer dosing.
Then reduce back again.
EI is not rigid, it's what you make of it and then use your own brain to modify for your management goals.
It's just a starting place or a method to rule other factors out.