As I said before, PH down for aquariums contains sulfuric acid, it is expensive for a bottle, and the label warns that it contains sulfuric acid. When used properly, it does no harm to the expensive exotic fish. In fact it keeps them alive as salt water exotics are VERY sensitive to the water conditions.
If your one who fishes rivers, streams, and lakes, you have no idea what run off chemicals you may be eating. Store bought tuna contains trace amounts of mercury. Muriatic acid aka hydrochloric acid is used in swimming pools to bring PH down and people swim in the water treated with it, even swallowing some, with no ill effects. That is the same acid used to etch concrete in high levels. It is excessive chlorine and uric acid (swimmers piss) that causes irritation of the skin, eyes, and lungs.
When it is used properly, it causes no harm. One aspirin can help a headache, take 30 of them it may be your last headache.
Read up on the chemicals that corporate farms use on the crops we eat. A small amount of sulfuric used to maintain ideal PH levels is nothing to be concerned about in the big picture.
For those who say, "I eat only organic products..." good luck with that. Whole Foods got caught selling modified food, even though they state they are all organic.