Another one excellent mineral for bananas is K-Mag. A few years ago, Harvey was kind enough to let us buy extra bags from him, it is very cheap by the 50-lb bag.
The most important feature is that it has very low chloride content, which is a big problem of KCl and supplies Mg and Sulfur. K-MAG is an excellent source of potassium, magnesium and sulfur that are used for custom blended fertilizers. Mined near Carlsbad, New Mexico, this naturally-occurring mineral known as langbeinite has a guaranteed analysis of 22% K20, 11% Mg (18% MgO) and 22% S.
Since the K analysis is actually 22% K2O, so it means that without counting the oxygen, it is 18% K. The KMag can be considered a natural organic fertilizer because it is not chemically synthesized, it is mined.
You can google for K-Mag
K-MAG Granular 0-0-22
It is also totally soluble forum, and thus you can really make a lot cheaper organic fertilizer blends for hydroponics, something like less than $1 per gallon.