Effectiveness of dosing systems (against corrosion)

We took over such a dosing system from our previous owner. The water pipes are from 1967, galvanized steel pipes. About 15 years ago, the pipes were apparently so clogged that a "pipe cleaning" was performed and a dosing system was installed. Now the pipes are clogged again; if the water stands for a few weeks, it comes out yellow-brown from the tap. At least from the taps where anything still comes out at all. We have now broken everything open and renewed the pipes; everything else makes no sense. The old pipes look pretty disgusting from the inside, I am glad they are out! So such a dosing system mainly costs a lot of money; I would rather question its usefulness. Oh, by the way; our water hardness is medium hard, I think that is also important to know.

Thank you for your feedback. A lot of money is relative, I think you have to invest a good 1000 EUR once (+ maintenance + dosing agents).

Our dosing system has chewed up a cartridge about every two months, so that quickly adds up to a nice sum. And as I said, I doubt whether the system has any measurable added value at all. I can upload an internal photo of the pipes next week. There is no sign of a protective film; there is just black gunk sticking to the walls.

Here are the promised pictures. The picture with the two pipes shows two T-pieces, one of which is completely closed. The slag is slowly starting to corrode; a few weeks ago it was still black. As already mentioned, a protective film is only present, if at all, in the non-visible area.

Thank you very much, that looks intense.

I would also rather renovate completely and remove all iron/cast iron pipes or just live with the gunk as long as it is functional. From a health perspective, I don't see any risk. At my parents' place, we also recently removed a water softening system. Connecting pipes made of cast iron look the same.

However, the water hardness is very high there, and the softening system was only retrofitted after two decades of service. I cannot assess to what extent this was already present or how it would have looked without the 15 years with a softening system.

The ongoing costs of dosing agents (due to various pipe materials) and desalination tablets, combined with system-related residual scaling of the fittings, were the reasons to completely dismantle it again.