Yes do another one after adding 3-4 gallons of water poured down into the water, not through the salt. Wait two hours and do the manual regeneration. And if you weren't using pellet salt, you wouldn't have that mush buildup.
Softeners always leave a few inches of water in the salt tank at the end of the brining cycle; it can't be sucked out. Then they either add the volume of water for the salt dose lbs for the next regeneration at the end of a regeneration (most do it that way) or, they wait to do that at the beginning of the next regeneration (that is best, like my Clack WS-1) but...
No one including my good buddy Biermech can tell you how much water your softener will add to that water during the brine fill cycle unless they know the salt dose lbs.. That is controlled by the number of lbs of salt (3lbs/gallon) that the control valve, or the cheap float controlled volume of the Famous water powered KINETICO, is programmed to use per regeneration. So, 15 lbs requires 5 gallons etc.. I think Biermech sells smaller softeners than I normally do, that must use more salt than my smaller softeners and many of my larger softeners. That's because I size for high salt efficiency.
Solar crystal salt is best.