Curious what happens when pH is too low in a pool?
Below, we’re going to define what “low pH” really means, what you can expect to happen when your pH drops too far, and if it’s safe to swim in a pool with a low pH.
What Is “Low” pH in a Pool?
The optimal pH level in a swimming pool is between 7.2 and 7.8, which is slightly basic.
Saltwater pools will naturally sit higher on that range due to additional aeration caused by a saltwater generator, but they’re still susceptible to low pH under the right conditions.
Either way, if your pH level is below 7.2, especially for sustained periods of time, you’re going to see some unwanted side effects.
What Happens if pH is too Low in a Pool?
As with high pH, there are a few distinct consequences of low pH that become more severe the further your pH falls.
Let’s cover them.
1. It Corrodes Your Equipment
Acidic water is corrosive to metals.
In fact, the more acidic your water, the more corrosive it becomes, and this can slowly wreak havoc on your pool equipment.
Any metal that touches your water is at risk, including basic fixtures like ladders and rails, as well as expensive machinery like pool filters and heaters (heaters are especially prone to damage from low pH water).
To make matters worse, low pH eventually lowers total alkalinity, and pool water is even more aggressive when total alkalinity is also low.
2. It Damages Your Pool Finish
Ever heard of etching or pitting?
This happens in pools when acidic water slowly eats away at plaster, leaving behind a rough and worn-looking surface.
Don’t think you’re safe with a vinyl liner pool, either.
3. It Burns Through Your Chlorine
The lower your pH level, the faster your chlorine gets used up.
This happens because, when chlorine is added to your pool water, it either becomes active chlorine or reserve chlorine.
Active chlorine is extremely effective at sanitizing the water but it gets used up quickly. Reserve chlorine is much weaker but it slowly takes the place of active chlorine as it gets used up.
So how exactly is chlorine divided out?
Well, the ratio of active chlorine in your water is going to be higher at lower pH levels, meaning you will start with less in reserve.
At a very high pH, you end up with so little active chlorine your water is as good as unprotected.
4. It Itches Your Skin and Stings Your Eyes
Realistically, this one is a bit of a stretch.
While you often hear that pH impacts the comfort of swimmers in the water, it would actually take an extremely low pH level for any ill effects to be felt.
Human skin fluctuates between a pH of 5.4 to 5.9, for example, so pool water would need to be significantly lower than that to cause itching.
While you may feel some mild stinging of the eyes before that, the more likely cause for eye irritation is used up chlorine (chloramine) – you know, the stuff that gives off that strong pool smell?
5. It Reduces Your pH Buffer
Total alkalinity is a pH buffer, meaning it absorbs changes in the water and effectively keeps your pH level stable.
However, as your pH falls, total alkalinity soon falls with it.
This happens because, as your water becomes acidic, it “burns through” bicarbonate–which makes up a big part of your total alkalinity—to create more carbonic acid.
The result is lower total alkalinity, a weaker pH buffer, and ultimately a more vulnerable pH level.
Can You Swim in a Pool with Low pH?
Yes, to an extent.
Unless you’re extremely sensitive to pH, you’re unlikely to feel the effects of acidic pool water until it becomes very acidic.
We’re talking about a pH level of well below 5, and a level that low is almost unheard of in the pool industry.
Instead, it’s the inefficiency of your sanitizer (such as chlorine) that poses more of a risk at lower pH levels, potentially leaving you exposed to all kinds of contaminants in the water.
Important: Many pH testing kits have a lower limit on their measurements, meaning anything lower will always come back as the minimum possible reading. If you get the minimum pH, use another test kit to find the true pH.
What Causes Low pH in a Pool?
It can be difficult to pinpoint what causes low pH in your pool. Fortunately, the list of likely reasons is short.
Here’s what to look out for:
- Low pH fill water, such as city water or well water.
- Rainwater from heavy storms.
- Lotions, sweat, and other acidic waste brought in by swimmers.
- High levels of sanitizer such as bromine or chlorine.
- Dichlor shock (slightly acidic at pH 6-7).
- Low total alkalinity (alkalinity influences pH).
Bring It Back Up!
Whether it’s too low or too high, an unbalanced pH level is always going to be a problem for your pool.
Rather than dwell on the consequences of letting your pH slide, it’s important to waste no time in raising it back up – so grab your test kit, your borax or soda ash, and get to work rebalancing your pH.