The TL;DR of Acid Rain.

If you’re in the North Eastern United States, acid rain COULD just possibly be a “thing”.
The active ingredients in Acid Rain are Sulfuric Acid and Nitric Oxides / Acids. These are caustic compounds
Acid rain is about 4.5 to 5.0 pH
But normal rain is about 5.0 to 6.0
If your town gets a LOT of settled-out pollution and RARE rain, then the “runoff” will be WORSE than if you have a LOT of rain on the same amount of settled out pollution.
The reason that Western States have “worse” acid rain is because Las Vegas makes a LOT of pollution which piles up pretty deep before the next, rare rain. Then, you get that sulfuric acid runoff “all at once”.
Acid Rain is much better now than it was twenty years ago.
If “Acid Rain” killed your fish it would be because acidic runoff entered the pond ALL AT ONE TIME (after a drought) or if the pond had no BUFFERING CAPACITY. The PH would test “crashed” with the dead fish.

I encountered this online, and I wanted to just kinda go through it and straighten out this issue. I worked a REAL case of Acid Rain in New Jersey and it’s a “thing” but it doesn’t really have to be. And it kills way fewer fish than you’d think.

“….we have had torrential storms over the last few weeks, and I have had fish die in many ponds, and every pond that I tested has high ph. and I am concerned that we had a major acid rain that caused the issues.”

This kind of thing makes me want to go lay down.

“Fish die in many ponds.”

“Every pond I tested”

They represent they tested MANY ponds and ALL of them had a high pH after a torrential rain. (Exactly the opposite of acid rain). But the implication is that morts attend acid rain in many of the high pH ponds with fish losses.

Look. Some ponds are quite green. That’s a lot of Chlorella / algae.They are super high surface area extremely metabolically active and prolific plants. It’s nighttime and at night, oxygen is being consumed.. It’s a little dangerous. But then, the next DAY it doesn’t get sunny, so the greenwater doesn’t STOP using oxygen and producing carbon dioxide. Oxygen levels are held at least a point under the safe range. Worse, the electrical to the submersible pump gets rained-in and the pump cuts off for a few hours. Oxygen levels get much lower. Mass mortalities can result.

Diagnosis: Acid rain. Nope. Not without a ridiculously low pH. And even then, the pH trough can be transient.“

This map shows where in the United States we see acid rain the most. It’s not everywhere. And really it’s a two point difference from regular rain, one of the BIG PROBLEMS is the elements in it, sulfuric acid and nitric acids.

This map shows something interesting to me. Did you know that “rain” all by itself has a low pH? Look at this map that suggests that rain is below 6.0 across most of it’s range in the United States. It makes sense that ANYWHERE in the US that you are, a good long rain could take a FEEBLE carbonate system (weak PH) and drop it pretty hard. Anywhere. (But the key to that is water that is FEEBLE and NOT BUFFERED)

This article is among MANY I looked at to “summarize” about Acid Rain. There’s nothing written by EPA or USFWS on “Acid Rain in Residential Ponds” but it’s not hard to put together from one of these synopses:

What is Acid Rain- – US EPA

In the first place, the United States Acid Rain issue is better than it was. It’s still a “thing” for sure but it’s not like it was in the seventies, eighties and nineties.