Shock calculator
How to Shock a 500 gallon Pool with non-chlorine shock
Updated 2026-05-22
Use this dose for a 500 gallon residential pool with non-chlorine shock (potassium peroxymonosulfate / MPS). Add at dusk so sunlight does not burn off the chlorine before it can do its work.
Routine maintenance
0.1 lb
Raises free chlorine by about 5 ppm.
Algae bloom
0.1 lb
2 to 3 times routine for visible algae.
Procedure
- Pre-dissolve granular shock in a 5 gallon bucket of pool water if your pool has a vinyl liner or sun-bleached floor.
- Pour slowly along the deep end with the pump running.
- Brush every surface, especially walls and steps where algae attaches.
- Run the pump 8 hours minimum, ideally overnight.
- Re-test free chlorine in the morning. Aim for 3 ppm or below before swimming.
Swim wait
2 hours (MPS does not add chlorine to the water).
Notes for this chemical
- MPS (potassium peroxymonosulfate) is the standard shock for bromine pools and spas.
- MPS regenerates bromide reserve into active free bromine — it does NOT add chlorine.
- Safe to swim within ~2 hours since chlorine residual is unchanged.
- Some test strips read MPS residual as combined chlorine — a special reagent neutralizes it for accurate CC testing.
Not sure if you need to shock?
Scan your test strip with PoolSense first. The app tells you exactly when shock is the right action, and how much.
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