I have a WaterFurnace Model ATV034D110NLT unit in service for 22 years. The heat exchanger likely needs acid cleaning. My question is what strength Muriatic acid (HCl ) do I need to use to do the cleaning. I have heard it should be around 10 %. Do I need any additives to remove the iron deposits. Should I recycle the acid after it comes out of the heat exchanger or should I use several new batches of acid. I plan on pumping it from 5 gal. pail with a transfer pump and collecting it in another pail. Well has following test results: Iron 0.1 mg/L , Ca CO3 230 mg/L , Fluoride 0.7 mg/L Looking at other piping shows a black deposit that sometimes flakes off. I believe it to be iron. Unit is 34,000 BTU or 2.833 ton. It is running at 6 to 6.5 GPM on well water 40 to 60 psi. @ 50 deg.F inlet and 40 deg.F outlet. Heat exchanger is Cupronickel coaxial. The Kilowatt-hrs use for a season have gone from 10,000 KWhr. to about 12,000 KWhr. in the last 2 to 3 yr.