I'd be a bit wary of using citric acid if there's a lot of scale. The one time I tried it (trying to be nice and gentle with the still after we replaced the element) it seemed to react with the scale, but then made fluffy and flaky blobs of white stuff (insoluble calcium citrate ?) that wouldn't react no matter how much more citric acid I added. (Eventually got rid of it with a combination of formic acid, and flushing with lots and lots of hot water !)Thanks for your suggestion. I'll certainly give it a go, although I'm based in London with VERY hard water! What concentration do you use?
Thank you for this very helpful reply, I'll try acetic tomorrow Yes, I do the boiling thing too!Same still model as yours:
Our tap water is insanely hard and thus our still needed at least a light clean every two weeks. Ideally we'd use 10% formic (keep it in there for about 2hrs before washing it out), but when our supplies are low we'd either default to store-bought vinegar or 1m acetic. The most difficult part is getting all the undissolved crud that forms at the bottom of the still out. Its a faff to dismantle it, so what I find myself doing is sending short high-powered water bursts through it and trying to wash it out through the stop-cock thing.
You can help the acid along a bit by heating it occasionally. I would put it on for 5 to 10 seconds at a time, careful not to start boiling it.
You could probably use citric, but I would stick to formic or acetic if you can