Substitute descaler/cleaners for coffee machines

Beenie

I have a Melitta automatic coffee machine. This means that that it uses whole coffee beans, grinds then brews internally, and then dispenses your drink. The internal pipework needs regular cleaning.

The branded liquid and cleaning tablets are expensive and difficult to find, mostly being sold online. I'd like to find a safe substitute and wondered if anyone had come across this problem before, and perhaps found something themselves?

The manufacturer states that the guarantee is invalid if you use anything other than their own brand of cleaner and descaler, so I really need someone who has done this themselves with no ill effect to their own coffee machine.

JIL

i have a tassimo, i have a cleaning disk that i have used with both vinegar and lemon juice.
i have also used this https://www.ocado.com/webshop/product/Ecozone-Kettle--Iron-Descaler/74264011?from=search&tags=%7C20000&param=descaler&parentContainer=SEARCHdescaler_SHELFVIEW when it was on half price offer and it worked well.