Vinegar has acetic acid in it, I dump 2/3 gallons of Vinegar in my empty water tank and run my system including my solution hose and wand,
Then turn it off and let it set over night.
Fill tank will fresh water in the morning and let it all flush out... be prepared to clean all of your screens out, they will be clogged with lime that didn't dissolve.
Also here is a quote from wikipedia on Descalers:
A descaling agent, also known as descaling, anti-limestone, anti-limescale, anti-lime, or anti-scale, is a solution to remove limescale, e.g. from water taps, kettles, toilets and water pipes. Descaling agents usually contain an acid as the active ingredient. They are available in liquid form, e.g. aqueous solutions of acetic acid, lactic acid, citric acid, sorbic acid, phosphoric acid, hydrochloric acid, sulfamic acid or in solid form, e.g. sodium bisulfate powder.
Descalers do not necessarily need to be acidic (although many are). Often the mechanism of descaling is done via chelation. Descalants of this sort can be the most powerful. Phosphonates in particular are well known scale inhibitors.