I empty the water from the toilet bowls, pour muriatic acid in the bowls, use rubber gloves, Comet powder or some other brand and I make the worse-looking toilets in about 10 minutes and make them look like they just cake out of the box.

If its well water , and the water is acidic , and you have copper pipes , you will get bluish stains in the sink , tub and toilet .

i've heard of boric acid?

If they put dishes in the dishwasher with slobs of butter, fatty chicken skin and artichoke hearts and these things got pushed down the drain and caused an obstruction, you have a reason to sit them down and have a conversation. 

I would have all the floors done in white concrete and acid stained for good looks, easy clean up and it will last long. 

I think the hardest part will be at closing, when you get that fatty 40k check and then ......you have to hand over 30,000 big ones to your partner because he did all the work.

It was non-acid stain, very easy to apply, and it looks amazing!

CIP deterioration is most negatively affected by soil issues (not applicable here), speed of flow through pipe (faster is better, within reason), and makeup of the effluent and gases within (mostly acidic for waste, possibly basic in heavy cleaning situations).

Batteries and battery acids are also common, dry cells and lead acid for larger models.

A typical electric water heater can make it 30 years easy if you just change the rods, unless you have super acidic water.