I would suggest Yara Actisil for a foliar spray.
Actisil is the one I have experience with. But I can not find it on the Yara USA website.
I will send them a mail today and ask if they have it in the US as well, or if they use a different name for it.
(The Yara site is down for a few hours:
Hi, we are performing some updates. We will be back online shortly! It is not a small company. They emply 17000 people worldwide and have a turnover of 13 billion $)
There are several products with Silicon/Silica.
Completely soluble in water for use in hydroponics, fertigation and foliar applications in agriculture and horticulture. PQ corp. AgSil® potassium silicate fertilizer offers growers these performance benefits in many agricultural applications: • Provides resistance to mineral stress. •...
customhydronutrients.com
These are powders that you have to mix to get a concentrate (always the cheapest)
But there is also this, by PQ as well, called SilMatrix.
Sil Matrix is a Silicon-based material used for natural control of fungal plant pathogens, insects and spider mites. Features multiple modes of action.
www.7springsfarm.com
Looks great to me. Not too much K, and a decent amount of SiO2.
It can be used in a tank and as foliar spray.
(it can rise your EC)
Avoid those typical cannabis brands. They always overcharge you for the exact same stuff.
If you look for example Plant Magic bio-silicon that
@plantastic mentioned.
It costs about $ 36 for a liter and it contains 14.3% SiO2.
SilMatrix costs about $ 8 for a liter and then it contains 20.8%SiO2.
So if you want to get rich, buy SilMatrix in bulk, repack it, name it
Aaron Silica Magic and sell it for $ 40 for a liter.
If I would live in the USA I would go for SilMatrix.
Also because it is widely available and there is a lot of info about it. And not just BroScience blabla but real data.