Well believe me or not but they do test GH on marijuana plants. They know that more then 80% of their business is to people growing marijuana. Advanced nutrients blends theirs just for marijuana and they publish their test results on how it works with marijuana. So when they say this amount at this cycle it's not just a guess.

Sure you can use to much but most people suffer from not enough and then miss diagnosis their problem as to much. They are just not using a proper balance of NPK fertilizer. Every strain is a little different and each cycle is a little different the grower needs to know how to tell the difference and that is where the problem comes in.

No; Silica Blast is not the same as thing. It does not replace potassium or even a supplement of potassium. The potassium silicate is meant to strengthen the cell wall and add vigor to the stock. Potash mixed with water is a boost for extra potassium.
You don't have a Potassium mobile problem dude I hope you don't think you do. Potassium problems are really hard to find because they run with several other problems that make it hard to know the difference.

From the looks of your pictures you have more of a toxic salt problem, probably just some nutrient build up around the root ball of one or two of the plants. Potassium deficiency show as more dark green leaves with black spots or red tips on the end of old leaves first.

If you don't follow their directions then it's hard to know if you have a full range of NPK fertilizers or not. The larger your reservoir is the more nutrients you can hold and the better the Ph buffers work and the less problems you have with nutrient lockout or toxic salts build up and Ph swings.

Puffy I think I answered you question too