How to Lower pH in a Pool

Aim to hold pH at 7.4 to 7.6. Readings from 7.2 up to 7.8 are all acceptable. Above 7.8 is too high, and that's when it's time to add a little acid and bring it back down.

Check total alkalinity too, if your test measures it. The target range is 80 to 120 ppm. Ppm is short for parts per million. It's simply a way of stating how much of something is dissolved in the water, and it's the figure your test reports.

How much acid you need comes down to how big your pool is. All of these doses call for 31.45% muriatic acid and work for pools with normal alkalinity. Each dose moves the pH from 7.8 down to 7.5.

Measure the dose for your pool rather than pouring straight from the jug.

For example, a 12 by 24 ft pool averaging 4.5 ft deep holds roughly 9,690 gallons. That's nearly 10,000 gallons, so 9 fl oz or so is the dose to use.

Add the acid where moving water carries it away fast. One thing that helps is a return jet, the small opening in the wall of the pool that sends filtered water back out into the pool.

1. 1. Start the pump and leave it on while you pour.
2. 2. Get your measurement ready beforehand. Acid always goes into water, never water into acid.
3. 3. Pour slowly, right in front of a return jet.
4. 4. Put in one chemical at a time, and keep acid and chlorine apart.

Give it 30 minutes with the pump on, then run another pH test. If the pH is still high, work out a new dose for your current reading, since the table only covers a drop from 7.8 to 7.5. If it has dropped below 7.2, soda ash will bring it back up.

Acid lowers alkalinity as well as pH, so the doses in the table work best when alkalinity is in its normal range of 80 to 120 ppm. If you keep adding acid often, check alkalinity too, because it may be drifting low. If your goal is to lower alkalinity itself, you'll need more acid: 26 fl oz (755 mL) drops it by 10 ppm in a 10,000-gallon pool.

Everything here is measured in US gallons, so knowing your pool's volume pays off. These popular sizes all assume the water averages 4.5 ft deep:

This website stores your gallon figure in your browser and plugs it into each dose calculator for you.

Not sure how many gallons you have? Find the closest size in the table, or multiply length by width by average depth, all in feet, then by 7.48 (use 5.9 for a round or oval pool). If the bottom slopes, average the depths by adding the shallow end to the deep end and dividing by 2.