To determine how much pH minus to use for your 6800-gallon pool with an alkalinity of 350, follow these steps:

1. Determine the current pH level of your pool water. This can be done using a test kit or a digital pH meter.

2. Calculate the difference between your desired pH level and your current pH level. The ideal pH range for a pool is between 7.2 and 7.8, so if your current pH is above 7.8, you will need to lower it.

3. Use the following formula to calculate the amount of pH minus you will need:

pH minus dose (in ounces) = (desired pH - current pH) x gallons of water x 0.016

4. Apply the pH minus directly to the pool water. It is best to add the pH minus slowly, while circulating the water, to avoid overdosing.

Example Calculation

Let's say that your current pH level is 8.0 and you want to lower it to 7.6. Using the formula above, we can calculate the amount of pH minus you will need:

pH minus dose (in ounces) = (7.6 - 8.0) x 6800 gallons x 0.016 = 17.92 ounces

Therefore, you will need to add approximately 17.92 ounces of pH minus to your pool water to lower the pH from 8.0 to 7.6.

Notes:

- It is important to follow the dosage instructions on the pH minus product label to avoid overdosing.

- Lower pH levels may irritate skin and eyes, so be sure not to add to the pool when swimmers are present.