Does algaecide expire?
Not quickly — its safety data sheet calls it stable under normal conditions of storage, and properly kept it holds potency up to 5 years. One winter in an unheated shed can end it anyway.
Updated
- Sealed
- Up to 5 years
- Opened
- 5 years, if it never freezes
Sealed: Up to 5 years Tier 3
Pool algaecides are among the more stable liquids on the shelf. The safety data sheet for a polyquaternium algaecide describes it as stable under normal conditions of use and storage, and In The Swim's figure for a bottle kept in a cool, dry indoor spot is potency held for up to 5 years. The conditions carry that number: above 75°F, or in direct sun, the lower-concentration 10% and 30% formulations fade first.
After opening: 5 years, if it never freezes Tier 3
Opening the bottle does not shorten the chemistry — the same 5-year figure applies to a capped, part-used bottle stored consistently cool. What shortens it is where the bottle then lives. In The Swim is blunt about the one that matters in a garage: freezing temperatures can ruin pool algaecide, and the product itself does not freeze until well below room temperature, so it takes a genuinely cold shed to do it.
How to tell it's gone off
- A bottle that has been somewhere it could freeze — In The Swim's warning is that freezing temperatures can ruin pool algaecide.
- Solids, cloudiness or a separated layer that stays put after the closed bottle is rocked.
- Where the bottle lived: a shelf that runs above 75°F or gets direct sun ages the 10% and 30% formulations fastest.
- A cap or neck crusted with dried product from repeated seasons.
If you use it anyway
Degraded performance
Algaecide is one of the steadier things on a pool shelf: its safety data sheet calls it stable under normal conditions of storage, and kept cool and dark it holds potency for years. The failure worth planning for is a bottle that froze. Ruined algaecide is still just a liquid in a bottle — it announces itself the following month as a green pool, not as any kind of hazard, and the cost is the dose you thought you had.
An algaecide's active chemistry sits happily in the bottle — its safety data sheet calls it stable under normal conditions of use and storage — so the calendar is not really the variable. Temperature is. Sustained heat above 75°F and direct sunlight wear down the weaker formulations, and a freeze can break the product outright rather than merely weaken it.
Every page here commits to one of four states — Harmless · Degraded performance · Equipment damage · Safety issue. How the verdicts work.
How to store it
The safety data sheet asks for one thing: store it in a cool, dry place, out of reach of children. In The Swim adds the two limits a garage actually tests — keep it under 75°F and out of direct sun, and never leave it where it can freeze.
Sources
- Tier 2 · SDS
Nava Water Products (Clearon) — Safety data sheet: ProTech Algaecide 60, sections 7, 9 and 10
Checked 2026-08-27. Polyquaternium 42 algaecide; source of the stability and cool-dry storage statements.
- Tier 3 · trade & standards
In The Swim — Chlorine shelf life: how long can I store pool chemicals?
Checked 2026-08-27. Pool-trade retailer; the 5-year figure and the freezing warning ship as Tier 3.