While testing I realized that the ink that I used caused a lot of corrosion on steel, copper, aluminum, and brass parts:

I assume this is caused by the sodium propionate that I used for increasing the conductivity of the ink.

Since the ink has to be conductive for the CIJ printing process, it needs to contain something that makes it this way and since all salts that I know so far can cause corrosion on metals like steel, copper, aluminum, and brass, these materials have to be replaced by other corrosion resistant materials like stainless steel, rubber, and plastic to prevent corrosion of the printer and also contamination of the ink.

So, I searched for corrosion-resistant fittings to replace all the brass fittings and ultimately stumbled across the Reverse Osmosis plumbing system of white fittings of all sorts + white 1/4 inch and 3/8 inch PE tubing.

I think with all brass parts replaced by plastic or stainless steel the printer should now no longer have problems with corrosion caused by a small amount of salt in the ink.

While the printer hydraulics should be fine now, the printhead is still made out of brass, copper, and aluminum and will also need an upgrade to withstand corrosion.