Guide
How to open a pool for the season
A pool opening checklist: equipment start-up, then the chemistry in order (alkalinity, pH, stabilizer, chlorine last), with opening-day targets and doses per 10,000 gallons and litres.
Updated · 4 min read
Opening a pool is two jobs. First the equipment: cover off, water up to the middle of the skimmer, pump and filter running. Then the chemistry, tested and corrected in order: total alkalinity, then pH, then stabilizer (CYA), then chlorine last, at dusk. Each product goes in separately, with the pump running, with a wait before the next. Plan on an afternoon plus a retest the next day.
Opening-day targets
For an outdoor plaster pool dosed with liquid chlorine or tablets; salt pools differ where noted.
| Reading | Target | Notes |
|---|---|---|
| Free chlorine | 5 to 7 ppm at CYA 40 | never below 3 at CYA 40; salt pools 5 to 10 at CYA 70 |
| pH | 7.2 to 7.8, aim for 7.6 | salt pools aim for 7.5 |
| Total alkalinity | 60 to 80 ppm | 80 to 120 for trichlor tablet pools |
| Calcium hardness | 250 to 650 ppm (plaster) | vinyl up to 550 and fiberglass up to 300, with no need to add any |
| CYA (stabilizer) | 30 to 60 ppm, aim for 40 | salt pools 60 to 80, aim for 70 |
| Salt (salt pools only) | 2,700 to 3,600 ppm, aim for 3,200 | or your cell's own range |
How to open your pool, step by step
- Clear the cover. Pump or siphon the water off the cover (never into the pool), then remove, clean and dry it.
- Refill to the normal level. Bring the water to the middle of the skimmer opening.
- Start the equipment. Reconnect and prime the pump, check for leaks, start the filter, and brush the walls and floor.
- Circulate, then test everything. After a few hours of running, test free chlorine, pH, TA, calcium, CYA and, for a salt pool, salt.
- Keep swimmers out if chlorine is very low. Below half the minimum for your CYA, the water isn't sanitized yet.
- Raise alkalinity first if it is low. Add baking soda separately, with the pump running, then wait an hour and retest.
- Correct pH second. Acid lowers it, soda ash raises it; add it separately, with the pump running, and wait 30 minutes before the next step.
- Add stabilizer third if CYA is low. Put it in a sock in the skimmer basket with the pump running. It takes up to 48 hours to dissolve; don't backwash or clean the filter for a week.
- Add chlorine last, at dusk. Dose it for the CYA you just added, not the CYA you measured. If the pool opened green, shock and hold instead.
- Salt pools: check salt before turning the cell on. If you add salt, keep the cell off for 24 hours; its reading takes about a day to catch up.
- Retest the next day and write the numbers down. Opening day is the baseline for the season.
Doses you're most likely to need
| Task | Per 10,000 US gal | Per 10,000 litres |
|---|---|---|
| Raise TA by 10 ppm (baking soda) | 1.4 lb | 168 g |
| Raise CYA by 10 ppm (stabilizer) | 13.4 oz | 100 g |
| Lower pH 7.8 to 7.5 at TA 80 (31.45% muriatic acid) | 8.0 fl oz | 62 mL |
| Raise free chlorine by 1 ppm (10% liquid chlorine) | 12.8 fl oz | 100 mL |
Why this order
Alkalinity holds pH in place, so it comes first, and the acid dose depends on it. Stabilizer comes before chlorine because the chlorine target depends on CYA. Chlorine goes in at dusk so the sun doesn't burn it off, and never at the same time as acid: acid and chlorine release chlorine gas when they meet. That's why every product goes in on its own, with a 30-minute wait between them.
When to open
Open before the weather turns warm. Untreated water grows algae faster as it warms, and a pool opened green takes far more chlorine to clear than one opened clear. In Australia the calendar is reversed, so opening comes in spring.
Questions people ask
Should I shock the pool when I open it?
Not by habit. Shock level is for a reason: visible algae, combined chlorine above 0.5 ppm, or more than 1 ppm of chlorine lost overnight. A clear pool that tests well just needs its normal target.
My cover water looks like a swamp. Now what?
Pump the cover dry first, never into the pool, then follow the checklist. Expect a bigger first chlorine dose, and possibly a shock and hold.
Do I add chlorine before or after stabilizer?
After. Stabilizer takes up to 48 hours to dissolve, but dose chlorine as if the CYA you added is already in the pool.
Anything different for a salt pool?
Test salt before powering the cell, keep the cell off for 24 hours after adding salt, and expect pH to climb once the cell runs. Chlorine targets are the salt-pool ones.
For an ordered plan with exact amounts from your opening-day test, enter your readings in the water check.