Pool shock is one of the most misunderstood chemicals in residential pool care. Owners use it too often, too little, mix incompatible types, or pick the wrong product for the problem they actually have. Done right, shocking your pool is the difference between water that’s a little dull and water that sparkles for weeks. Here’s how to pick the right shock for your pool.
What “shock” actually does
Shocking a pool means raising free chlorine to a level high enough to break the chemical bonds in chloramines (combined chlorine, the stuff that causes the “chlorine smell” and stinging eyes) and oxidize organic contaminants. It is not a routine sanitizer dose — it’s a periodic reset.
There are three main shock chemistries you’ll see on the shelf, each with a clear use case:
1. Calcium Hypochlorite (cal-hypo) — the heavy hitter
Typically 65–73% available chlorine. Fast-acting, unstabilized, and the most common choice for routine weekly shocking. Will temporarily raise calcium hardness and cloudy water if dumped directly — always pre-dissolve in a bucket of water before adding to the pool. Best for plaster, gunite, and concrete pools.
2. Dichlor — the stabilized option
Around 56% available chlorine plus built-in stabilizer (cyanuric acid). Dissolves clear without clouding, no pre-dissolving required. Stabilizer is a plus for outdoor pools at the start of the season but becomes a liability if you use it weekly — cyanuric acid only goes up, it never goes down without dilution. Best for occasional shocks on vinyl and fiberglass pools.
3. Non-chlorine shock (potassium monopersulfate) — the swim-ready option
Oxidizes organic contaminants without adding chlorine. Lets you swim within 15 minutes of adding instead of waiting for chlorine to drop back to swimmable levels. Won’t kill algae or break chloramines as effectively as chlorinated shock, so use as a supplement rather than a primary sanitizer. Great after a pool party when you want clear water by morning.
How much to add
The standard residential shock dose is 1 lb of cal-hypo per 10,000 gallons of water, which raises free chlorine roughly 5–10 ppm. Dichlor doses higher per pound for the same effect (about 1.5 lb per 10,000 gal). Read the label — concentrations vary by brand. Always add shock with the pump running, in the evening, and around the perimeter of the pool, not all in one spot.
Our top picks at PST
These four products cover every residential shocking scenario, from a quick weekly maintenance dose to a heavy-duty algae kill:
Durachlor 1 Lb Assault 73 Granular Shock
Shop Now
Pool Season 2 Lb Chlorinating Concentrate
Shop Now
Pool Season 25 Lb Chlorinating Concentrate Pail
Shop Now
Pool Season 50 Lb Chlorinating Concentrate
Shop NowCommon mistakes
- Adding shock directly to a vinyl liner. Undissolved cal-hypo granules can bleach the liner. Always pre-dissolve in a bucket of pool water and pour the solution around the perimeter.
- Mixing shock with anything besides water. Never mix shock with other chemicals in a bucket — it can react violently. One product, one bucket, one pour.
- Shocking during the day. UV destroys unstabilized chlorine within hours. Always shock in the evening so it has all night to work.
- Skipping the brush. Algae anchors to surfaces — shock alone won’t kill it. Brush the pool walls first, then shock.
Not sure which one?
If you’re shopping for a single shock to keep on the shelf, the Durachlor Assault 73 cal-hypo is the workhorse pick. For high-volume regular maintenance, the Pool Season pails are the cheaper per-pound option. Reach out to PST Pool Supplies and we’ll match the right shock to your pool size, surface, and chemistry profile.