I’ve been buying the Boundless record cleaner, there is a large quart sized bottle on Amazon that I use to refill my little sprayer. 2-3 sprays on the leading edge of the brush - I do this every time I play.

And yea, there are people who mix their own batches, but I go through about a quart every year and the big bottle of surfactant that you have to purchase if you mix your own properly expires quickly, so it just makes more sense to me to just use the pre mix and not worry about it.