The H3PO4 I mix with water and detergent from Aldi. It should be an acidic detergent, for example one with a basic Zitronensäure.Bei be clumping the surfactants. Careful when mixing. Protect eyes and hands, use goggles and rubber gloves and an empty small irrigation bottle. Only 1/2 water, 1/3 detergent and only then add some H3PO4. Not flipped H3PO4 always on the water. It does not necessarily have to be filled with H3PO4, you can also use sparingly. Less can also have as their object much. Dissolves lime, rust, urine scale of the fixtures, the toilet and in the shower in no time. Does not smell like ammonia, can not be upheld as hydrochloric acid to the chromium plating, their vapors unnoticed attack other metal parts in space. Water from old galvanized pipes like leaves rusty rivulets in toilet etc. This is also easy to get rid of it. Can be used as rust remover on all steel and iron products. So do not be a hero, but always diluted using it. Only the water and then carefully add the acid.
