After reading @lefthandseeds comment on the silica for hydro thread I got to thinking. Having a hard time finding pure potassium silicate in stores, time to figure out how to follow these dosages with cheaper more abundant products.
I first considered ANs Rhino skin so I will compare.
Please chime in if something is incorrect, my off the cuff maths and chemistry has much to be improved upon.
Hardware store liquid potassium silicate for sealing concrete, seems like the same stuff, just unknown concentration.
One brands safety sheet states 3.2mole, hey no fair, I`m not a chemist 
.
Googlefu to the rescue, i hope.
Oh and dont buy the ones with soap and solvent in them, saw several products like that.
Molar mass of K2SiO3 = 154.2803 g/mol
1l of the hardware store stuff would then contain 3.2x154g= ~500g/l
Potassium silicate contains 18.204% Si and 50.685% potassium (K).
500*0,18= 90grams of silica, 250g of potassium in 1lit.
30-50% by weight looks to be standard for this type of product according to multiple MSDFs.
30mg is 30ppm in a liter, 300mg in 10 liters, ~2g in 65l(17gal).
Soooo, ummm, highschool math is failing me.
18% is close enough to .2, five times more stuff to get to 1.
2g to 65 liters needs 10grams actual potassium silicate.
50% solution has 0.5grams per milliliter.
30ppm Si02 dosage for 65 liters = 20ml from said bottle (30% solution need 33ml)
0,3ml/lit 50% solution, 0,5ml/l 30% solution.
If I didn’t goof my calculations, Advanced nutrients Rhino skin recommends 2ml/l, that would mean they may be selling a 4x weaker solution, ~7.5% at ~42$/l(EU), ~25$/l(US) .
Of course they could have a higher aim say 100ppm SiO2 instead of my conservative 30ppm meaning its a 30-50% solution at 42$ vs 9$, sheesh.
The NPK of Rhino skin is a clue, 0 - 0 - 0,4.
Agsil 16H potassium silicate powder is 0 - 0 - 32 
Agsil is 80x stronger than Rhino skin, thats a pretty big difference.
Assuming Agsil is like any other potassium silicate, half a kilo of it would equal the cement sealant ,it would then be 0 - 0 - 14, 40x more potassium than Rhino.
That would make Rhino a 1.25% solution.
If thats true you would need 12ml/l of Rhino to reach the same 30ppm of SiO2 that the 50% cement sealant can do at 0.3ml/l.
I was wrong, just found Rhino skin pdf, Silicate acid, potassium silicate1312-76-1<0.1%(lessthan0.1%)
Hard to believe, is there something magical with Rhino I missed beyond potassium silicate?
European Ebay.
7.5€(9$) for a quart/1lit.
5-10l sizes are 2-3€(2.5-3.5$)/liter/quart.
5l jug will do 250x 65l reservoirs, not bad, thats ~5 years with weekly reload.
