Green pool water is algae — plain and simple. It's one of the most dramatic pool problems you'll face, but it's also very fixable. The approach depends on how bad it is, so let's start by figuring out what you're dealing with.
Before adding anything, test pH, chlorine, and alkalinity. You need pH between 7.2-7.6 for shock to work effectively. If pH is above 7.8, lower it first with muriatic acid — otherwise you'll waste your shock.
Brush the walls, floor, and steps thoroughly before shocking. Algae clings to surfaces and brushing loosens it so the shock can reach and kill it. Don't skip this step — it makes a real difference.
Use cal-hypo shock at these amounts based on severity:
Always shock at dusk. Pre-dissolve in a bucket of water before adding to the pool.
Run your pump and filter 24/7 until the water clears. This is non-negotiable — the filter is what physically removes the dead algae from the water. If you have a sand filter, backwash every 12-24 hours as pressure builds up.
💡 The water will turn cloudy or grey before it turns clear. That's actually a good sign — it means the shock killed the algae. Keep the filter running and it'll clear up.
A maintenance dose of algaecide after shocking helps kill any remaining algae and prevents regrowth. Add it the day after shocking, not at the same time — chlorine will destroy it if you add them together.
Once the water is clear, test all your chemistry and get everything back in balance. Heavy shocking often raises pH — you'll likely need to add some acid to bring it back down.
If you're fighting algae repeatedly, the root cause is usually one of these:
⚠️ Don't swim in green water. Algae itself isn't particularly dangerous, but the bacteria that thrive alongside it can be. Keep everyone out until the water is clear and chlorine is back to 1-3 ppm.
Describe what your pool looks like and Wade will give you a personalized treatment plan based on your pool size, water type, and equipment.
Try PoolBoy Free for 14 Days