Backyard Aquaponics
A place to discuss aquaponics

Everyone seems to have forgotten about potassium silicate.

First I've heard of it.

How much does it cost and is it "organic"?

I believe potassium silicate is a foliar spray mainly.. but coming to the type I use in my system is K2SO4 or potassium sulphate.. and I buffer with calcium hydroxide because where I'm from. potassium buffer is very hard to find. KCl is fine too but you the chloride will start slowly accumulate within system.. and well wood ash is available.

I didn't think hydroxides buffered the pH rather they just lowered it?

Your right they don’t,they don’t lower it either,PH for Pot Hydroxide is 13.0 Calcium is 12.4.

I meant raise it to counter the acidity from nitrification. Oops.

I use the API phosphate test kit. I tried to source potassium silicate a while back, though due to restriction on sale of fertiliser in WA its near impossible to get hold of. I'd like to try it, I know some organic nurseries use it in their 'rock dust' mix.

I did the math on KCl, would need to add a truck load of it to get the Cl concentration up to similar levels people generally dose their systems with (using NaCl). That said I'm struggling in WA to get find a source for K Silicate, K Nitrate or K Cl. I've not been able to find out any upper limit for where Sulphate becomes an issue, but I'm guessing there must be one?

I originally thought potassium nitrate was not an option due to the nitrate adding to high nitrate levels, but you do get 3 times as much K as nitrate with it so it does give a 'residue' free form of supplementation for high ph systems. (eg does not leave Chloride or Sulphate ions that may not be used in the system and build up)

I did some research no sulphate toxicity and really didn't come up with much results.. most of the article says that plants can consume excess sulphate without any negative effects other that extra sulfur in the plants.. it may actually be beneficial for consumption.. but I'm not entirely sure.. but nevertheless I use K2SO4 for potassium and on occasion MgSO4 for magnesium..

ps if you got potassium hydroxide.. or potassium carbonates or potassium bicarbonate.. just mix it with muratic acid to produce KCl.. its that simple.

Be extremely careful if mixing HCl with KOH! Its' a strongly exothermic reaction and should be done with the proper precautions. If you don't know what these are, it's best not to try it!

Re adding K2SO4, it may well increase acidity a bit, certainly that's the effect of adding Sulphur to soil gardens.

Says the man who was talking about adding metallic potassium

I did suggest eye protection be used!

It's not cheap. 2.5 Gallons weighs 25lbs, and costs $135. Sil-Matrix is the only NOP compliant silicate product out there. The more common and less expensive Ag-Sil (powder) is not. Apparently the silicate is cheap to source from metal slag, which is considered non-organic. The silica used in the manufacture of potassium silicate must be sourced from naturally occurring sand.

The way the differentiate between the two is that the organic form is aqueous. And it's not allowed for nutrition purposes, but as a "Crop pest, weed, or disease control". Funny how stronger plant cell walls lead to less mildew....

Little cost comparison:
To raise silica by 50ppm in a 1000L system:
Ag-SIl 16H: 200g, $5.70
Sil-Matrix: 1 L, $13.50

Big thumbs up for potassium nitrate. If your system is kicking along - the extra nitrate is of little/no consequence, imho. Plus I love the smell of potassium nitrate in the morning. It smells... like victory...