A solid chemical feed unit dissolver has an upper feed unit chamber with an inwardly tapering sealing surface at its lower end and against which a lowermost feed unit seals, retaining the upper chamber in a dry condition, preventing wetting and caking of solid chemical feed units behind the dissolving and sealed off face of the solid chemical feed unit. A solid chemical feed unit magazine is slotted to permit gentle feeding of a plurality of solid chemical feed units therein and a cover-defined sight slot permits guiding and visual observation of remaining solid chemical feed units in the magazine. The magazine preferably, but not necessarily, defines the tapering sealing surface. Distinctly shaped solid chemical feed units are disclosed. The dissolver can handle large solid chemical feed unit loads up to one hundred pounds or more and in a small footprint stable configuration. Methods are disclosed.