Water – How to clean water softer salt tank without disconnecting

As a guess, the pipes got layered internally in scale, that will come out over some time (dissolving into the now softer water). Some large chunks may require filter screens, shower heads and valves to be soaked in your vinegar or CLR (containing lactic and gluconic acids).

I know boilers get descaling treatment, but I've not heard of the same with standard pipes. If they were quickly descaled, there might be a large amount of debris, which would necessitate disassembly (washer inlet filters, refrigerator water connections, shower valves, toilet valves). Perhaps all the hose hookup devices could be disconnected for the treatment

1) The crystals are most likely deposits left from the evaporation of water that used to be in the tank (as you mentioned, you had the lid off). As the water evaporated, the dissolved minerals transitioned into their natural crystalline structure, which is attractive to the dissolved minerals -- rinse and repeat and you have a larger crystal structure adhered to the wall.

2) You could -- but from the look, my personal preference would be to empty it and give it a good and thorough cleaning.

3) A thorough cleaning once a year is often recommended. Is it necessary? Maybe not, but it couldn't hurt anything either. I'm sure your owner's manual outlines a deep cleaning procedure, but if not, there are a number of resources on the internet.

Regarding the disinfection -- I would follow the manufacturers recommendations. You should use a fragrence-free bleach. Store-brand bleaches often have less additives than Clorox, which is good when the use is "food"-related. Clorox uses additives which aid in the removal of soils (things like caustic soda, soda ash), surfactants, and other ingredients to help prevent stains (sodium polyacrylate). 4 oz does seem a bit much, but the manufacturer would know better than me what should be used.

4) I'm not sure why your manual does not recommend the mixture of potassium chloride and sodium chloride -- these are mixed in water softeners quite often to decrease the saltiness of the drinking water and save a bit of money. My vote is, when in doubt, follow the manufacturers recommendations -- they only spent millions developing the thing (of course, they would also like to make money when you need to replace it, so it's a bit of a double-edged sword).