Water Chemistry /
What increases alkalinity in a pool?
Pool alkalinity usually rises from alkalinity-raising chemicals, high-alkalinity fill water, or repeated water-balance adjustments that gradually shift total alkalinity upward.
Archive date: this article was written for PoolSkimmer on Oct 23, 2026 and given the earlier archive date of Feb 22, 2026 so the blog reads as an organized archive. It was not published on that date.
What is driving up pool alkalinity?
There are a few ways for the alkalinity in a pool to go up. It can be the result of an alkaline chemical being put in, or perhaps the fill water you are using has its share of buffering minerals. Even routine water-balance work can have the effect of shifting the chemistry higher over time. The prudent thing to do is to test the water and consult your equipment manual and the product label before making any changes.
Common culprits
For the most part, total alkalinity in a swimming pool will rise for one of these reasons:
- Alkalinity increaser or baking soda put in to correct low levels
- Fill water with high alkalinity when refilling or topping off
- Going after the pH repeatedly, which in turn alters the balance
- Topping off often after rain or splash-out, bringing in new source water
Sodium bicarbonate, or baking soda, is a staple for raising alkalinity. But it can also put a little upward pressure on the pH depending on your water, so retesting is in order.
Spotting an increase
You will want to use a test kit or strips to see if there is a pattern. Be on the lookout for total alkalinity numbers that are on the climb from one test to the next, or a pH that is becoming difficult to pin down. You may notice the water getting cloudy or some scale-like deposits as the balance drifts, and your usual chemical adjustments might not seem to do the trick. Do not rely on a single reading; make sure the circulation has done its job of mixing the water before you test again.
Where to start
A good rule of thumb is to follow this order of operations:
1. Get a reliable read on the pH and total alkalinity with a drop test or strips. 2. Go over what has been added of late – shock, stain treatment, baking soda and the like. 3. Consider the source water if the pool has been drained or topped off recently. 4. Verify the filtration and circulation are in order so the water is well mixed for your next test. 5. Before doing anything else, put your results up against the product label and manual.
And remember, if you need to clean out the skimmer basket, shut the pump off. One should never put a hand in operating suction equipment.
Things that don’t raise it directly
Certain chores are good for keeping the water in check but they are not going to drive alkalinity up on their own. Brushing, vacuuming and skimming will improve clarity and circulation, and filter care ensures even mixing. Aeration is more likely to move the pH than the total alkalinity. Still, without proper maintenance you may find your tests are not truly representative of the pool.
When to bring in a pro
If you are at a loss as to why the alkalinity is climbing, or the pH is all over the place no matter what you do, it is time to call a qualified professional. The same goes if you are seeing persistent imbalance, cloudiness or scale, or if you have a hunch there is something wrong with the plumbing or filtration. If you are not certain what was put in the water last, let them handle it.
Pitfalls to steer clear of
Do not add chemicals on a hunch or mix them together. Never work on the equipment while the pump is running and pay attention to the labels and manuals. And if the water does not appear safe or there is any question of an electrical issue, keep swimmers out until a professional has had a look.
Sources and further reading
- [Hayward: Weekly pool maintenance](https://www.hayward.com/maintenance/weekly-pool-maintenance)