If you dose a fair amount of NO3 via KNO3, keep nice tank parameters, don't have much fish load, I'd suspect you don't need to add K separately.
Steve and I did this for awhile, there were times when folks could not get any K2SO4 around the area, so we did without.

We never really found much difference.Steve suggested we did not need any extra K as it was being supplied via KNO3.

If you have 6.4 ppm of so of NO3, then you add 4 ppm of K using KNO3. Some products have K+, like TMG.
I find it unlikely you really need MORE K+ to grow plants well and ************it's one less thing that folks need to dose which is my goal here****.
Looking at a mass balance of N/K+ ratios, __most/many__ plants have about 1.5 :1 ratios of N:K(Epstien 1972).

Now take into account the O3 part of NO3 and to get elemental N and you suddenly find you have plenty of K+ for plant growth.
So 1.5/4.4= .34 N's for every K+ you add.

So you should theoretically have 3x as much K as you need relative to N x the 1.5/1 ratio = 4.5x as much K+ relative to N per dose.
.
There are other sources of N, plant decomposition, fish waste but some K+ comes from these pools also.
I really do doubt that adding K2SO4 to such a tank will make any significant difference.

Unlike NO3 and denitrifying bacteria NO3=>N2 gas, there is not much to the K+ cycle except for plant uptake/leaching.

So it certainly is something folks can skip if they add KNO3 as their main source of N.

Now if you have a good fish load, over feed Discus, slow growth/non CO2 etc, adding K+ from KCl/K2SO4 is advisable since you already will have plenty of NO3.

But for many, KNO3 as the source of both N and K should do the trick.

I'd say you simply don't need but 3 things, KH2PO4, KNO3 and traces.
And then the other two parts: Light and CO2.

I'm glad Ghori brought it up as I've not thought about it since I guess 1997 or so. But going through it, it should not be a problem even with all the different plant species needs and possible extra K+ needs a plant might have.

I think it's be EVEN easier for the new folks and us too, to delete one more nutrient from the mix.

That is a GOOD GOAL.

The goal is to reduce down with simpler designs/methods/dosing routines for folks that still work very well.

Importantly:
Just remember if you have NO3 issues from the tap/fish load, you will still find a use for K+ dosing from KCl or K2SO4.

Regards,
Tom Barr

how would NO3 issues show themselves (for future reference)?

In terms of too low or too high?

Regards,
Tom Barr

Beeing a plantgod, you may give details of both (how about that ).

I'm not a plant God, just a plant Gremlin: Too much and the fish die. Too little and the plants die. OK?

Too low, BGA, too high dead shrimp.

Regards,
Tom Barr

ahh. That might be the reason why my amanos keep dying on me! Ill try less KNO3 and adding some K2SO4 instead.

Thank you Gremlin and T-Rex (oh did I say that out loud? )

Let's give some ranges there so folks misinterpt the information as is the common way of the web............

Too low,: under 2-5ppm.
Too high: well over 100ppm from KNO3 for 3 days or more. Noter: no fish has any issues with this level.

Regards,
Tom Barr

Ya, I was reading one of your articles where you provided some information about what kind of fluctuance in dosing is considered "ok". Over 100ppm KNO3 is alot and obiously not what I have in my tank. Hence something else must be killing my amanos.. I wonder if they are sensitive to CO2.

Amanos are sensitive to CO2, more so than many smaller fish.
Also NH4/NO2.

They make good "guinea pigs" for test therefore.

Low O2 will also kill them.

So some decent surface current is wise.

The high levels of NO3 I made mention of are really outside most anyone's dosing routines, so there's seldom an upper limit issue and I'd be very surprised to see one personally.

To date I have never heard of someone killing their fish with too much KNO3.
So I'm doing well with the sugegstions and ranges, although there are a lot of folks Crying, moaning, whining on and on about how high levels of "pollutants" like NO3 will harm their fish with EI dosing, to date not one person has shown what such levels are or are not nor shown any evdence that the NO3 from KNO3 is toxic to fish etc within a wide range or an upper range.

Not one person(other than myself).

Regards,
Tom Barr