How Do I Raise Alkalinity in a Pool?

To raise total alkalinity, add sodium bicarbonate, which is ordinary baking soda sold in pool stores as alkalinity increaser. Roughly 1.5 pounds per 10,000 gallons raises total alkalinity about 10 ppm. Broadcast it slowly across the deep end with the pump running, let it circulate at least six hours, then retest.

Target range is 80 to 120 ppm. Aim for the upper half (100 to 120 ppm) if you have a saltwater system or a plaster pool.

Why alkalinity matters more than people think

Total alkalinity is the water’s buffer. It is what keeps pH from lurching every time you add a chemical, get a rainstorm, or run the heater.

When alkalinity drops below 80 ppm you get pH bounce: readings swing from 7.0 to 8.0 and back with almost nothing added. Chasing pH in that situation is futile. Fix alkalinity first and pH becomes stable and easy to hold.

Low alkalinity also makes water corrosive. It will etch plaster, stain surfaces, and go after metal fittings and heater exchangers.

Doing it right, step by step

1. Test total alkalinity with a drop kit. Strips are not precise enough for this.
2. Calculate the gap. If you read 60 ppm and want 100 ppm, that is 40 ppm. In a 15,000 gallon pool that is roughly 9 pounds of baking soda.
3. Split large doses. Never add more than about 4 pounds per 10,000 gallons at one time. Add, wait six hours, retest, repeat.
4. Broadcast it across the deep end with the pump on high. Do not dump it in one pile, which just settles on the floor.
5. Brush the floor if you see any undissolved residue.
6. Retest after a full turnover, ideally the next day.

Baking soda vs soda ash

These get confused constantly.

• Sodium bicarbonate (baking soda) raises alkalinity strongly and pH only slightly. This is what you want for an alkalinity problem.
• Sodium carbonate (soda ash) raises pH strongly and alkalinity somewhat. Use this when pH is your problem.

If alkalinity is low and pH is also low, baking soda often brings both into range on its own. If alkalinity is low but pH is already high, use baking soda anyway and correct pH afterward with a small amount of acid, or better, let aeration settle it.

What is draining your alkalinity

If you are adding baking soda every week, look for a cause:

• Heavy trichlor tablet use (trichlor is acidic and eats alkalinity continuously)
• Frequent acid additions to fight high pH
• Rainwater dilution, especially prolonged heavy rain
• Recent large water replacement or a refill
• Bromine systems and some mineral sanitizers

Key West specifics

FKAA fill water in the Keys carries meaningful alkalinity, so topping off a pool here tends to push alkalinity up rather than down. That means a Keys pool testing low on alkalinity usually has an active cause, most often a tablet feeder running hard or repeated acid dosing to hold down pH.

Storm season is the other driver. A single heavy summer rain can dump enough water into an open pool to dilute alkalinity noticeably overnight, and after a tropical system passes it is worth running a full test rather than assuming your last set of numbers still holds. With no freeze and no closing season, our pools never get the winter break that lets mainland chemistry sit still.

Get alkalinity into range before you touch pH, because a stable buffer turns pH from a weekly fight into a number that mostly takes care of itself.