[Smeagol]

Obviously, KNO3 and KH2PO4 include Potassium. So why do some people also dose K2SO4? Is the Potassium in KNO3 and KH2PO4 not enough? What are the pros/cons of adding the extra Potassium? And what's the best way to know if you need to do it or not?

 

[Shremph]

I was seeing some potassium deficiency in leaves (pinholes) dosing the suggested regiment of KN03 and KH2P04 so I decided to add K2S04 instead of upping KN03 since I was already where I wanted to be with nitrates. Kh2P04 is fairly low in potassium so I didn't up that dosage either. K2S04 is a great option for some who lack potassium. The addition solved my problem.

 

[BraveBuc]

Yes exactly and toxic levels are super high if not impossible to reach. Raising your TDS is the only downside I can think of.

Edit: Oh, it can be a pita to dissolve in a dosing container. It also tends to make the tank water look cloudy for a bit.

 

[Raymond S.]

And KH2PO4 is the one fert that can be overdone easily.
I use half and half on my EI dosing/w K2SO4/KNO3 instead of full KNO3 amount listed
to help keep down the nitrates.

 

[Zapins]

Obviously, KNO3 and KH2PO4 include Potassium. So why do some people also dose K2SO4?

Because some species require more potassium than nitrogen and so KNO3 alone isn't enough.

Because reaching adequate K levels using KNO3 or KH2PO4 sometimes raises the nitrate and phosphate concentration to undesirable levels for fish and shrimp.

Is the Potassium in KNO3 and KH2PO4 not enough? What are the pros/cons of adding the extra Potassium?

I'd recommend incorporating K2SO4 in your fertilizer regimen rather than relying on KNO3 and KH2PO4. You may or may not have enough potassium without using K2SO4, but using it will not hurt and it ensures you won't have deficiencies.

And what's the best way to know if you need to do it or not?

Holes surrounded by a chlorotic margin on older leaves is a sign of acute potassium deficiency, though plants can often have a "hidden hunger" for nutrients without showing acute signs. In these situations growth slows considerably until enough of the missing nutrient is added back.

 

[Smeagol]

Okay, great. I have already been dosing K2SO4 along with KNO3 and KH2PO4, but I didn't know if it was really necessary or not. I will continue to use it, since the potential benefits seem to be far more likely than any potential harm. Thanks for the info.