If your pool’s gone a bit cloudy, smells a bit off, or someone just had a cannonball party weekend, it’s probably time to give it a shock. Now if you’re wondering whether nighttime’s the right time—yeah, it actually is. And here’s why.

So, pool shock (or pool chlorination) is when you dump in a higher-than-usual dose of chlorine to kill algae, bacteria, or whatever’s lurking in there. But here’s the trick—chlorine gets chewed up by sunlight real quick. That’s why shocking your pool during the day is kinda like putting sunscreen on before a swim and rinsing it straight off. A waste of time and money.

Here’s what matters: Do it at night. That way, the chlorine actually gets a chance to work properly without the sun breaking it down.

What time exactly? Wait for the sun to be completely gone—like, after dusk. The sweet spot is around 8:30pm–10:00pm depending on the time of year. By then the pool’s probably not being used, the UV rays are done for the day, and the chemicals can do their job properly. Easy as.

Now, before you go chucking shock in your pool, a few quick things:

Test Your Water First
Don’t guess. Grab a test kit or take a sample to your local pool shop—places like Pools & Spas NZ or your local Mitre 10 usually stock water testing strips or can do it for you. You’ll want to know your current chlorine levels, pH, and alkalinity.

Wait for the right conditions: Weather and water clarity play a role too. Don’t shock if a storm’s coming or if the wind’s kicking up loads of leaves and dirt into the pool.

How Much Shock to Use
Comes down to how grubby the water is. If it’s just routine maintenance, one standard dose (follow the instructions on the back of the bag—it’s not one-size-fits-all) per 40,000L works. But if the pool’s gone full swamp-mode (hello green water), you’ll need to go heavier.

Where to Buy Pool Shock in NZ
You can grab pool shock from places like Bunnings, Trade Tested, Mitre 10, or specialty stores like Pool & Spa Maintenance Services (Auckland-based but can deliver nationally). Just make sure it’s labelled “pool shock” or “chlorine shock” and not general purpose bleach (not the same thing).

Here’s what you should do:

1. Run your filter for 8–12 hours after shocking. This helps circulate the chemicals and clears out dead nasties.
2. Keep pets and people out of the water overnight. Even if it looks fine in the morning, test the water again before jumping in.
3. Do this regularly—once every 1–2 weeks during swimming season keeps your pool in top shape.

It’s kind of like changing the sheets on your bed. You might not think it matters after just one weekend, but once you get into the habit, you’ll notice the difference big time.

Oh, and another tip—store your shock somewhere cool and dry, away from kids and pets. You don’t want that stuff leaking or getting damp. It can get reactive if it’s not stored right.

Anyway, if you’re serious about keeping your pool clean and safe to swim in, night-time shocking is a no-brainer. Less sun = more effective chlorine = clearer water. Simple as that.