Chemical cost scales almost linearly with volume, which is why the first number worth getting right is how many gallons the pool actually holds — not its length and width.
Typical season, by pool size
A five-month outdoor season, moderate use, no cover:
| Pool | Volume | Chlorine | Balancers | Algaecide + misc | Season total |
|---|---|---|---|---|---|
| 15 ft round, above ground | 5,000 gal | $110–170 | $35–60 | $25–45 | $170–275 |
| 18 × 33 ft oval | 13,500 gal | $230–350 | $60–100 | $40–70 | $330–520 |
| 16 × 32 ft in-ground | 19,000 gal | $300–470 | $80–130 | $50–90 | $430–690 |
| 20 × 40 ft in-ground | 30,000 gal | $460–720 | $110–180 | $70–120 | $640–1,020 |
Chlorine is 60–70% of the bill in every row. Everything else is rounding by comparison, which is where the savings have to come from.
Where the chlorine actually goes
Not into killing anything. On a sunny day, UV destroys 1–2 ppm of free chlorine, and on an unstabilised pool it can strip half the free chlorine in about two hours.
That is the whole reason cyanuric acid exists. At 30–50 ppm CYA, UV loss drops by roughly 75% — the single largest lever on the bill, and it costs $25–40 once a season.
Too much is its own problem: above about 100 ppm the chlorine is so tightly bound it stops working, and the only fix is draining and refilling. See cyanuric acid too high.
Which chlorine to buy
Cost per pound of available chlorine, not per pound of product:
| Product | Available Cl | Adds CYA | Effective cost |
|---|---|---|---|
| Liquid (10–12%) | 10–12% | no | cheapest per lb, heavy to carry, loses strength on the shelf |
| Cal-hypo (65–73%) | 65–73% | no | cheap, adds calcium hardness |
| Dichlor (56%) | 56% | yes | convenient, drives CYA up fast |
| Trichlor tabs (90%) | 90% | yes | most convenient, drives CYA up fastest |
Trichlor tabs are the default because they sit in a floater and need no thought. They also add roughly 6 ppm of CYA for every 10 ppm of chlorine delivered — which is why so many pools reach August with CYA at 120 and chlorine that will not hold. Running tabs all season and then draining a third of the pool to fix the stabiliser is a false economy.
The two habits that halve the bill
1. A cover. A solar cover cuts evaporation, and evaporation carries chemicals out with the water. It also blocks UV. Typical saving on chemicals alone is 30–50%, and it pays for itself in one season on anything above 15,000 gallons.
2. Test, then dose. Shocking on a schedule rather than on a reading is how pools end up over-chlorinated and under-stabilised at the same time. A decent test kit is $30–60 once and it changes what you buy every week — see the chlorine dose calculator for the amount a given ppm rise actually needs.
What not to spend on
Algaecide as prevention. A pool holding proper free chlorine for its CYA level does not grow algae. Weekly algaecide is treating a symptom that correct chlorine already prevents, and copper-based products stain plaster.
Clarifier and flocculant every week. Cloudy water is almost always a filtration or chemistry problem. Clearing it chemically each week is paying to hide a filter that needs backwashing or a chlorine level that is too low for the stabiliser in the water.