| Pool Appearance | Algae Severity | Expected Time to Clear |
|---|---|---|
| Slight green tint, still transparent | Light | 24 hours |
| Visible green, floor barely visible | Moderate | 48–72 hours |
| Dark green, floor not visible | Severe | 3–5 days |
| Black or dark green with slime | Extreme | 5–7+ days or drain |
Test pH immediately. Adjust to 7.2–7.4 with muriatic acid if above that range. At pH 7.4, chlorine is 55% active. At pH 8.0, only 21% is active. This single step determines whether your shock will work.
Also test CYA. If above 80 ppm, partial drain before shocking — the shock will largely fail at high CYA.
Brush walls, steps, corners, floor — everywhere. This disrupts algae colonies and exposes them to the chlorinated water. Do not skip this. Brushing is the physical component that shock alone cannot replace.
Keep the pump running without interruption. Continuous filtration removes dead algae as the shock kills it. Clean the filter or backwash every 6–8 hours during treatment.
If the pool is turning from green to cloudy/grey or blue-grey — that is a success signal. The algae is dead and being filtered out. If still green, re-shock at the same dose.
Once the pool is mostly cloudy with dead algae on the floor: vacuum slowly and directly to waste (bypassing the filter). This prevents clogging the filter and removes the dead matter faster. Refill water level as needed.
Add a pool clarifier to help the filter capture any remaining fine particles. Run the pump continuously. The pool should clear to crystal blue within 48 hours for light-moderate algae.
The green → cloudy → clear progression is normal and means the treatment is working. Many people panic when the pool turns white or grey after shocking, thinking something went wrong. It has not — that is dead algae being filtered out. Patience and continuous filtration get you to clear water.
Log shock doses, chemistry readings, and filter pressure during algae treatment. PoolLens shows you the progression and tells you when to re-shock or add clarifier.
Open PoolLens Free →Calcium hypochlorite shock at high doses (2–4 lbs per 10,000 gallons) with pH at 7.2–7.4, combined with continuous filtration and aggressive brushing. Algaecide alone is too slow for an established algae bloom.
Light green: 2 lbs per 10,000 gallons. Moderate green: 3 lbs. Dark green or black: 4–5 lbs in multiple treatments. Always adjust pH to 7.2–7.4 before shocking.
This is a good sign. Shock kills algae cells, which become fine white particles suspended in the water — causing temporary cloudiness. The filter removes these particles, clearing the water. Green → cloudy → clear is the correct treatment arc.
Use shock (calcium hypochlorite) as the primary treatment. Algaecide is a preventive tool or secondary treatment. Add algaecide 24 hours after the shock to help prevent recurrence — not as a replacement for shock.
Yes — vacuum dead algae to waste 24 hours after shocking. This removes the dead matter faster than filtration alone and prevents clogging the filter with large amounts of algae. Set the multiport valve to "waste" for this step if you have a sand filter.