That's like doing the laundry with a drop of detergent. When diluted in the pool water, the oxalic acid in the formula is below the level of oxalic acid in spinach and rhubarb. We calculated that you would have to drink over 1900 gallons of pool water to get enough oxalic to be toxic. Of course, you wouldn't have survived the water. It doesn't matter whether you run the pump or not.
Some people like to dump the product directly on the stain with the pump off.
It's faster and more dramatic but can cause temporary streaking. The product is acidic and can lower the pH. You may also witness a temporary loss of chlorine residual. Just gently chlorinate. As little as 3ppm is enough to cause staining. United has made high residuals a thing of the past.