Potassium silicate would
probably work, and it doesn't necessarily need to be liquid, but you are vastly overcomplicating the subject

The Brightwell product is extremely expensive for what it is (diluted sodium silicate solution) considering you can buy technical grade water glass for about $10/500mL (instead of $10 for 125mL of dilute solution). Then again, you don't need to dose much solution, and when dosed undiluted, it immediately precipitates magnesium in the aquarium, though that is temporary and it will redissolve into the tank in a few minutes. To mitigate this I would mix 1mL of sodium silicate solution into about 200mL of water (either tap or RO, whichever was on hand) and would dose that, and no significant precipitate would form.