Quick verdict
The foundational balancer — get alkalinity right and pH behaves. Plain sodium bicarbonate at a fair price.
Ideal for
- Pools with low or unstable alkalinity
- Owners fighting bouncing pH
- Any pool type including salt
Not ideal for
- Pools already at 80–120 ppm alkalinity
- Lowering alkalinity (use pH Reducer)
The full picture
Total alkalinity is the unsung hero of pool chemistry: it buffers pH so it stops swinging every time you add a chemical or it rains. When alkalinity is low (below ~80 ppm), pH becomes unstable and hard to hold. In The Swim Alkalinity Increaser is 100% sodium bicarbonate — the same thing as baking soda, just packaged for pools — that raises TA into the ideal 80–120 ppm range. Balance alkalinity first and pH management gets dramatically easier. Dose it evenly with the pump running (about 1.5 lb per 10,000 gallons raises TA ~10 ppm) and retest. If you buy one balancing chemical to start, many pros say make it this one.
In The Swim Alkalinity Increaser (Sodium Bicarbonate, 25 lb) at a glance
- Type
- Alkalinity increaser (raises total alkalinity)
- How often
- As needed to reach 80–120 ppm TA
- Size / volume
- 25 lb
- Active ingredient
- 100% sodium bicarbonate
- Coverage
- ~1.5 lb per 10,000 gal raises TA ~10 ppm
- Compatible pools
- All pool types, including salt
- Safety
- Add slowly to pool water; keep from children; don’t mix with other chemicals.
- Storage
- Store cool, dry, and sealed.
Source: Compiled from manufacturer specifications, label directions, industry practice, and aggregated owner feedback. Follow label instructions; specs and prices change — confirm before buying.
This is a research-based review — our analysis draws on manufacturer specifications, manuals, warranty terms, and verified owner feedback rather than our own hands-on testing, and we note where a detail couldn't be confirmed. How we review
The in-depth review
Total alkalinity is the unsung hero of pool chemistry: it buffers pH so it stops bouncing every time you add a chemical or it rains. In The Swim Alkalinity Increaser is how you set it.
Why alkalinity comes first
When alkalinity is low (below ~80 ppm), pH becomes unstable and won't hold no matter how much pH adjuster you add. Set total alkalinity into the ideal 80–120 ppm range first, and every subsequent pH tweak gets easier and lasts longer. That's why many pros say if you buy one balancing chemical to start, make it this one.
What it is and how to use it
It's 100% sodium bicarbonate — chemically the same as baking soda, packaged for pools. About 1.5 lb per 10,000 gallons raises TA roughly 10 ppm; add it evenly with the pump running and retest. It nudges pH up slightly too, which is usually fine and easily trimmed with a little pH Reducer if needed.
Who needs it
Any pool with low or unstable alkalinity, and anyone tired of chasing a pH that won't stay put. If your alkalinity is already in range, you don't need it — and to lower high alkalinity, you'd use pH Reducer instead.
Performance breakdown
Research-based editorial judgments from specs, warranty terms, and verified owner feedback — not lab measurements. How we score
Pros and cons
What works
- Stabilizes bouncing pH
- Pure sodium bicarbonate, no filler
- Cheap and universally available
- Works in all pool types
What doesn't
- Slightly raises pH too
- Same as baking soda (you pay for packaging)
- Over-dosing can cloud water
- Won’t fix a pH-only problem
Best alternatives to In The Swim Alkalinity Increaser (Sodium Bicarbonate, 25 lb)
HTH
HTH Super Shock Treatment (Cal-Hypo, 1 lb bags)
Best default shock
Widely available calcium hypochlorite shock that raises chlorine fast without adding cyanuric acid — the right default for most pools.
Taylor
Reagent Refill Set
Taylor
Taylor Reagent Refill Set
Best kit refresh
Fresh reagents for your Taylor kit — because expired reagents read wrong, not just weak.
In The Swim
pH Increaser
In The Swim
In The Swim pH Increaser (Soda Ash, 25 lb)
Raise pH
Granular soda ash to bring low pH back up — the fix when your water tests acidic and starts eating equipment and comfort.
In The Swim
pH Reducer
In The Swim
In The Swim pH Reducer (Sodium Bisulfate, 30 lb)
Lower pH
Dry acid granules to bring high pH and alkalinity down — safer to handle than liquid muriatic acid.
Frequently asked questions
Is this just baking soda?
Chemically, yes — it’s 100% sodium bicarbonate, the same active as baking soda. Pool packaging is convenient in bulk; some owners use food-grade baking soda instead, though purity and consistency can vary.
Why balance alkalinity before pH?
Alkalinity buffers pH. If TA is low, pH swings wildly and won’t hold. Setting TA into the 80–120 ppm range first makes every subsequent pH adjustment easier and longer-lasting.
How much raises my alkalinity?
About 1.5 lb per 10,000 gallons raises total alkalinity roughly 10 ppm. Add it evenly with the pump running, wait, and retest — our alkalinity calculator helps you dial in the exact dose.
Does it raise pH too?
A little — sodium bicarbonate nudges pH upward while mainly moving alkalinity. That’s usually fine; if pH climbs too high afterward, a small dose of pH Reducer brings it back.
Can I use it in a salt pool?
Yes — it works in all pool types, and salt pools benefit from solid alkalinity to counter their tendency to drift high in pH.
My alkalinity is too high — does this help?
No — this raises alkalinity. To lower high alkalinity, use pH Reducer (sodium bisulfate), ideally dosed in a concentrated spot with aeration to bring TA down while limiting the pH drop.