A pool's chemical budget is dominated by one line — the sanitiser — and everything else is rounding. Which makes the sanitiser decision worth more thought than the other four lines put together.
The figures below are for a 20,000 gallon outdoor pool over a 22-week season, at 2026 retail prices.
Sanitiser
Chlorine demand in an outdoor pool runs roughly 2–4 ppm per day in peak sun, and closer to 1.5 ppm in the shoulder months. Over 22 weeks, call it a season total of 350–420 ppm of free chlorine delivered.
| Product | Cost per ppm per 10k gal | Season total, 20k gal |
|---|---|---|
| Liquid chlorine, 10% | $0.31 | $230 |
| Bleach, 8.25% retail | $0.52 | $385 |
| Trichlor tablets | $0.44 | $325 |
| Cal-hypo, 73% | $0.48 | $355 |
| Dichlor, 56% | $0.71 | $525 |
| Salt system, electricity only | $0.06 | $45 |
Two things fall out immediately.
Liquid chlorine is the cheapest bulk chemical, bought in 2×2.5 gal cases from a pool store rather than as retail bleach — the concentration difference alone is most of the gap.
A salt system is cheaper than everything, on chemicals. It is also $1,400–2,200 to install with a cell that costs $500–900 to replace every 4–7 years, so the honest annual figure is nearer $150–250. The full comparison is worth working through properly.
Tablets look competitive on this table and are not, for a reason that does not appear on it — see below.
The rest of the budget
| Line | Season |
|---|---|
| Muriatic acid, pH control | $40–70 |
| Alkalinity increaser | $20–35 |
| Calcium hardness increaser | $0–40 |
| Cyanuric acid, if starting from zero | $25–40 |
| Shock, 4–6 events | $50–90 |
| Algaecide | $0–60 |
| Test reagents or strips | $30–55 |
| Filter cleaner | $15–25 |
| Subtotal | $180–415 |
A salt pool adds $60–120 of salt in the first year and very little afterward, and it uses noticeably more acid, because chlorine generation drives pH up continuously. Budget $80–120 of acid on a salt pool rather than $40–70.
Season totals
| Setup | Sanitiser | Everything else | Total |
|---|---|---|---|
| Liquid chlorine | $230 | $250 | $480 |
| Trichlor tablets | $325 | $230 | $555 |
| Cal-hypo | $355 | $220 | $575 |
| Retail bleach | $385 | $250 | $635 |
| Salt, consumables only | $45 | $310 | $355 |
Anyone spending materially more than $700 a season on a pool this size is buying something the pool does not need, and it is usually algaecide, clarifier and phosphate remover — the three products with the highest margin and the lowest necessity in a pool whose chlorine is held correctly.
The two decisions that move the total
1. Tablets or not. Trichlor is convenient, and every tablet adds cyanuric acid — about 6 ppm of CYA for every 10 ppm of free chlorine delivered. A season of tablets adds 40–60 ppm of CYA to a 20,000 gallon pool.
That is not a one-season cost. Higher CYA means more chlorine required to do the same work, so year two's chlorine line rises, and year three's rises again, until the pool needs draining. The tablet budget above understates the true cost by more each year it continues.
2. A cover. A solar cover costs $80–200 and cuts evaporation by 50–70%. Evaporation carries chlorine away, so a covered pool uses roughly 25–40% less sanitiser — $60–90 a season here — on top of the heating saving, which is much larger still.
What overspending usually looks like
Chasing a reading. A pool with high CYA reads adequate free chlorine and still grows algae, so the owner buys algaecide, then clarifier, then phosphate remover, and the total climbs past $900 while the actual problem — a number on the CYA test — goes unaddressed for the whole season.
The diagnostic is why chlorine can read high in a green pool, and it costs nothing to check.
Where the season budget sits in the whole
Chemicals are typically 20–30% of a pool's annual running cost. Electricity for the pump and heat for the water are larger, and both respond to equipment choices rather than to shopping — the full picture is in the monthly running cost.