A summer storm can undo a week of perfect pool chemistry in a few hours. Here is exactly how to get it back: the right shock type, the right dose, and the step-by-step recovery process from murky green to crystal clear.
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What You Need: Primary product: Premium Swimming Pool Shock, 24 x 1 lb Bags ($109.99) For brushing: Shop Pool Brushes at PoolPartsToGo For filtration: Shop Filter Systems at PoolPartsToGo |
What a Storm Actually Does to Your Pool Chemistry
Most pool owners see a green or cloudy pool after a storm and reach straight for shock. That instinct is correct, but treating without understanding what went wrong means you will often under-dose, miss a pH problem that makes the shock ineffective, or chase clarity that never quite arrives. Here is what is actually happening to your water during and after a storm:
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What Enters the Pool |
Contaminant Type |
Primary Effect |
Urgency |
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Rainwater (acidic) |
pH disruptor |
Drops pH and alkalinity; chlorine becomes less effective at low pH |
Treat within 24 hours |
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Runoff (dirt, lawn chemicals, debris) |
Organic load |
Consumes free chlorine rapidly; feeds algae spores |
Treat within 24 hours |
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Wind-blown debris (leaves, pollen, insects) |
Organic load |
Adds nitrogen and phosphorus; algae food source |
Remove and treat within 24 hours |
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Floodwater (if pool overflows) |
Bacteria and pathogens |
Introduces fecal bacteria, E. coli risk; renders pool unsafe |
Treat before any swimming |
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Dilution from heavy rain |
Chemical dilution |
Drops chlorine, alkalinity, and calcium hardness levels |
Test and rebalance before swimming |
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Sunlight after storm clears |
UV degradation |
Destroys unstabilized chlorine 4x faster in bright sun |
Shock in the evening for maximum contact time |
The most critical interaction in the table above is pH and chlorine effectiveness. Chlorine efficiency drops dramatically as pH rises above 7.6. At pH 8.0, your chlorine is only about 20 percent active. Rainwater is naturally acidic (often pH 5.5 to 6.5), which sounds helpful, but the combination of acidic rain plus organic runoff plus dilution creates an unstable environment where chlorine gets consumed almost as fast as you add it. This is why testing pH before shocking is not optional.
Why Shock Type Matters: Cal Hypo vs. Trichlor vs. Dichlor
Not all pool shock is the same, and the type you choose significantly affects your outcome, especially after a storm. There are three common shock types:
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Calcium Hypochlorite (Cal Hypo) 65 to 78% (What Power Shock Uses) The professional standard for shock treatment. Fast-acting, high-concentration, and stabilizer-free. Does not add cyanuric acid (CYA) to your pool, which is critical if your CYA levels are already elevated. Best for storm recovery, algae treatment, and opening a pool. Power Shock uses 68% Cal Hypo in full 1 lb bags. • 68% active ingredient (full strength, not shrinkflated) • Stabilizer-free: will not raise CYA levels • Works quickly: visible improvement typically within 24 hours • Safe for inground and above-ground pools Best for: post-storm, green water, algae blooms, pool openings, and any situation requiring a strong sanitizing dose. |
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Trichlor (Trichloroisocyanuric Acid) 90% High concentration but adds CYA with every dose. Used primarily in tablet form for regular maintenance, not as a shock product. Using Trichlor to shock a pool repeatedly will cause CYA to climb above safe levels (over 80 ppm), at which point you need a partial drain to correct it. Best for: routine maintenance tablets only. Not recommended for storm recovery or heavy shock treatment. |
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Dichlor (Sodium Dichloro-s-Triazinetrione) 56 to 62% Granular, fast-dissolving, and pH-neutral. Does add CYA, though less than Trichlor. Useful for spot treatments and vinyl liner pools where direct broadcasting of Cal Hypo granules carries a slight bleaching risk if granules sit undissolved on the liner. Lower active concentration than Cal Hypo. Best for: vinyl liner pools where direct Cal Hypo contact is a concern. Still adds CYA, so use sparingly. |
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A Note on Vinyl Liner Pools and Cal Hypo: Calcium Hypochlorite granules can bleach a vinyl liner if they settle on it undissolved. To avoid this, broadcast Power Shock over the deep end while the pump is running and walk the perimeter as you pour rather than dumping from one spot. Some pool owners pre-dissolve Cal Hypo in a bucket of water before adding it, though the Power Shock label specifies broadcasting directly. If you have a vinyl liner, broadcasting with good distribution while the pump is running is the safest approach. |
Your Post-Storm Chemistry Targets
Before you apply a single bag of shock, test your water and record where every parameter stands. Here are the targets you are working toward, in order of priority:
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Parameter |
Ideal Range |
Post-Storm Priority |
Why It Matters |
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Free Chlorine |
1.0 to 3.0 ppm |
FIRST |
Sanitizes the water and kills bacteria. Rain and organic load will have consumed most of your available chlorine. |
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pH |
7.2 to 7.6 |
SECOND |
Controls how effective chlorine is. At pH 8.0, chlorine is only 20% active. Always adjust pH before or alongside shock. |
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Total Alkalinity |
80 to 120 ppm |
THIRD |
Stabilizes pH so it does not swing after adding chemicals. Rainwater almost always drops alkalinity. |
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Calcium Hardness |
200 to 400 ppm |
FOURTH |
Prevents plaster etching and scale formation. Dilution from heavy rain reduces hardness. |
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Cyanuric Acid (CYA) |
30 to 50 ppm |
CHECK |
Stabilizes chlorine against UV. Power Shock is CYA-free so it will not raise this level. If already over 80 ppm, do a partial drain. |
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Combined Chlorine |
0 ppm (under 0.5) |
CHECK |
Combined chlorine (chloramines) causes that strong 'chlorine smell.' Shock breaks it apart. If your pool smells strongly of chlorine, that is a sign you need to shock. |
The order matters. Adjusting pH before shocking is the single most common mistake pool owners skip. A pool with pH of 8.0 or above will consume your shock without ever reaching effective sanitizing levels. Bring pH into the 7.2 to 7.4 range first, then shock.
How Much Shock to Use: Dosing Guide by Pool Size and Situation
Power Shock is 68% Cal Hypo in 1 lb pre-measured bags. The standard dosing baseline is 1 lb per 10,000 gallons for a routine maintenance shock. Post-storm and recovery situations require more. Use this table to determine your starting dose:
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Situation |
10,000 gal |
20,000 gal |
30,000 gal |
Notes |
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Weekly maintenance |
1 lb |
2 lbs |
3 lbs |
Standard preventive dose. Add weekly after heavy use or on a fixed schedule. |
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Post-storm (light rain, clear water) |
1 lb |
2 lbs |
3 lbs |
Minimum dose after any rain event. Test first; if chlorine is near zero, use this as a starting point. |
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Post-storm (cloudy or murky water) |
2 lbs |
4 lbs |
6 lbs |
Double dose for visible cloudiness. Run filter 24/7 and reassess after 24 hours. |
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Green water (algae bloom) |
3 lbs |
6 lbs |
9 lbs |
Triple dose for active algae. Brush walls and floor before and after application. May need to repeat. |
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Floodwater contamination |
3 lbs |
6 lbs |
9 lbs |
Treat as a full algae recovery. Do not swim until water tests clear and free chlorine reads 1 to 3 ppm. |
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Opening after winter |
2 lbs |
4 lbs |
6 lbs |
Double dose to break down combined chlorine and organics from winter cover runoff. |
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How to Find Your Pool's Volume Rectangular pool: Length x Width x Average Depth x 7.5 = gallons Round pool: Diameter x Diameter x Average Depth x 5.9 = gallons Oval pool: Length x Width x Average Depth x 6.7 = gallons Average depth = (shallow end depth + deep end depth) divided by 2. For an irregularly shaped pool, most pool builders or service companies will have the volume on record. |
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The 24-Count Box Does the Math for You A 24-count box of Power Shock treats: 24,000 gallons at the standard maintenance dose, 12,000 gallons at a double (storm recovery) dose, or 8,000 gallons at a triple (algae/flood) dose. For a typical 15,000 to 20,000 gallon inground pool, one box gets you through multiple shock treatments across a season, including 4 to 6 weekly maintenance doses and 1 to 2 full recovery events. |
The 9-Step Post-Storm Treatment Process
This is the same sequence a pool professional would follow after a significant rain event. Follow the steps in order. Skipping steps (especially pH adjustment before shocking) is the most common reason pool recovery takes longer than it should.
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1 |
Wait for the storm to fully pass Do not treat the pool while it is still raining. New rain will continue to dilute chemicals and add contaminants. Wait until the storm is over and give the water a few hours to settle before starting any treatment. Tip: If flooding is a concern, check your water level first. An overfilled pool needs to be partially drained before you can rebalance chemistry effectively. |
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2 |
Remove debris from the water Use a leaf net or skimmer to pull out leaves, insects, branches, and any other visible debris. Do this before adding any chemicals. Organic debris will rapidly consume the shock you apply, wasting product and slowing recovery. Also empty skimmer baskets and the pump strainer basket. Tip: A pool brush is useful here too. Brush walls and the floor to loosen any algae that may have started forming, which brings it into suspension where the filter and shock can handle it. |
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3 |
Test your water chemistry Use test strips or a liquid test kit to measure free chlorine, pH, total alkalinity, and cyanuric acid. Write down the readings before you touch anything. Post-storm water commonly shows: free chlorine near zero, pH below 7.2 (acidic from rain), and alkalinity lower than normal. These numbers tell you exactly how much you need to add. Tip: If you do not have a test kit, most pool supply stores offer free water testing. Take a sample in a clean container from elbow depth, away from the return jets. |
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4 |
Adjust pH and alkalinity first Shock is most effective at pH 7.2 to 7.4. If your pH is below 7.2, add sodium carbonate (soda ash) to bring it up. If alkalinity is below 80 ppm, add sodium bicarbonate (baking soda) first, since raising alkalinity will also nudge pH upward. Let the pump circulate for at least 30 minutes after any pH adjustment before adding shock. Tip: Never add shock and pH adjusters at the same time. Always run the pump between chemical additions. |
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5 |
Apply Power Shock at the correct dose With the pump running, broadcast the contents of each Power Shock bag evenly over the deep end of the pool. Walk around the perimeter as you pour to distribute it across the surface rather than dumping it all in one spot. Use the dosing table in this article to determine how many bags to use based on your pool size and the severity of the problem. Tip: Power Shock is 68% Cal Hypo. Do not pre-dissolve in a bucket. Broadcast directly as directed on the label. For very green water (heavy algae), brush the walls and floor before and immediately after application. |
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6 |
Run your filter continuously for at least 24 hours Shock works by oxidizing contaminants, but your filter removes the dead organic matter and suspended particles that follow. Keeping the filter running continuously is not optional for storm recovery. If your filter pressure rises 8 to 10 psi above its normal operating pressure during this period, backwash a sand filter or clean a cartridge filter to restore flow rate. Tip: If your pump is showing any signs of strain (unusual noise, reduced flow, overheating), this is a good time to confirm it is sized correctly for your pool. Inground variable speed pumps handle continuous low-speed operation far more efficiently than single-speed models. |
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7 |
Brush walls and floor again after 12 to 24 hours After the first round of shock has had time to work, do a second brush pass to knock loose any algae or residue that has settled on the surfaces. This brings it back into the water column where filtration can remove it. For plaster and gunite pools, use a stiff nylon brush. For vinyl liner pools, use a soft or ultra-soft brush to avoid surface damage. Tip: The Blue Torrent pool brushes in PPTG's collection use 360-degree bristle design that contacts corners and curved surfaces other flat brushes miss. See the pool brush collection link in the products section below. |
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8 |
Re-test and rebalance 24 hours after shocking Test all parameters again at the 24-hour mark: free chlorine, pH, alkalinity, and calcium hardness. Free chlorine should be in the 1 to 3 ppm range. If it has dropped below 1 ppm and water is still cloudy, apply a standard maintenance dose (1 lb per 10,000 gallons) and run the filter another 24 hours. Rebalance any parameters that are still outside the target range. |
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9 |
Confirm clearance before allowing swimming The pool is safe to swim when free chlorine reads between 1 and 3 ppm, pH is between 7.2 and 7.6, the water is clear enough to see the bottom at the deep end, and there are no visible algae patches on walls or floor. Do not rely on water color alone. Cloudy water can look clear under certain lighting but still carry contaminant levels above safe limits. Tip: The standard guidance is to wait at least 24 hours after shock treatment before swimming. With a 68% Cal Hypo product like Power Shock, this applies regardless of how clear the water looks. |
The Green-to-Clean Recovery Timeline
For pools that are visibly green or heavily cloudy after a storm, here is a realistic day-by-day guide for what to expect and what to do:
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Day |
Expected Appearance |
Action Required |
Products Needed |
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Day 1 (storm hits) |
Cloudy, green tint, or murky. Possible debris. |
Remove visible debris. Test chemistry. Adjust pH to 7.2 to 7.4. Apply shock at double or triple dose depending on color. Run filter 24/7. |
PPTG Power Shock (2 to 3 bags per 10,000 gal). Pool brush for walls and floor. |
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Day 2 |
Lighter green or cloudy blue-gray. |
Re-test chlorine. If below 1 ppm, re-shock at standard dose. Brush walls and floor again. Keep filter running. |
PPTG Power Shock (1 to 2 bags per 10,000 gal if needed). Pool brush. |
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Day 3 |
Cloudy blue or milky white. |
Cloudiness at this stage means dead algae in suspension. Filter is processing it. Keep running. Backwash or clean filter if pressure has risen 8 to 10 psi above normal. |
Pool brush. No additional shock usually needed. |
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Day 4 to 5 |
Clearing noticeably. Light blue haze. |
Test all chemistry (chlorine, pH, alkalinity, hardness). Rebalance as needed. Continue running filter. |
Standard dose of shock if chlorine dips below 1 ppm. |
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Day 6 to 7 |
Clear or near-clear water. |
Final chemistry test. Confirm: free chlorine 1 to 3 ppm, pH 7.2 to 7.6, alkalinity 80 to 120 ppm. Pool is safe to swim when all readings are in range. |
No shock needed. Brush for final pass. |
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When to Call a Professional If your water is still visibly green or cloudy after 7 days of treatment with correct dosing and continuous filtration, it is worth calling a pool service professional. Black algae (which appears as dark spots on plaster, not green water) requires a specialized treatment approach that goes beyond shock. Similarly, if your CYA is above 100 ppm, a partial drain and refill is usually the only practical fix, and a professional can advise on the safest way to do it without damaging your equipment. |
Products on PoolPartsToGo
Pool Shock
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Blue Torrent (Power Shock) $109.99 (was $189.99) Premium Swimming Pool Shock, 1 lb Packs (24 Count) Full-strength 68% Calcium Hypochlorite in pre-measured 1 lb bags. Stabilizer-free formula will not raise cyanuric acid levels. Fast-acting for storm recovery, algae treatment, pool opening, and weekly maintenance. 24 bags per box. Suitable for inground and above-ground pools. Broadcast directly over the deep end with pump running. Ships free. |
Pool Brushes (Essential for Algae and Storm Treatment)
Brushing before and after shock treatment is not optional for storm recovery. It loosens algae from surfaces and brings it into suspension where the shock and filter can handle it. PPTG carries multiple brush sizes and bristle types:
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Blue Torrent (Best for Plaster and Gunite) $26.99 (was $38.99) 360-Degree Bristles Blue Torrent Pool Brush 18 Inch Patented 360-degree bristle design reaches corners and curved surfaces that flat brushes miss. 18-inch head for fast coverage on walls and floor. Professional-grade. Stiff nylon bristles suitable for plaster and concrete surfaces. Best for inground pools and any situation where algae is clinging to textured surfaces. |
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Blue Torrent (Best for Vinyl Liner Pools) $26.99 (was $38.99) Ultra-Soft 360-Degree Bristles Blue Torrent Pool Brush 18 Inch Same 360-degree bristle design as the standard model, with ultra-soft bristles that will not scratch or scuff vinyl liner surfaces. Recommended for above-ground and inground vinyl liner pools, especially when using Cal Hypo shock. 18-inch head. Patented and professional-endorsed. |
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PoolPartsToGo (Best Value Maintenance Bundle) $79.99 (was $139.99) Heavy Duty 360 Maintenance Kit The complete pool maintenance kit for post-storm recovery and ongoing upkeep. Combines the heavy-duty 360-degree brush with additional cleaning tools in one discounted bundle. Ideal for pool owners who want a single purchase that covers brushing, skimming, and general maintenance after storm events or algae recovery. |
Frequently Asked Questions
How soon after a storm should I shock my pool?
As soon as the storm is fully over. The longer you wait, the more organic matter from debris and runoff will consume your existing chlorine and feed algae growth. Treat within 24 hours for a standard rain event. For flooding or overflow events, treat as soon as the water level stabilizes and the storm has passed. Do not wait for the water to turn green before acting.
My pool smells strongly of chlorine after the storm. Does that mean I have too much chlorine?
Counterintuitively, a strong chlorine smell usually means you do not have enough usable chlorine. The smell comes from chloramines (combined chlorine), which are the byproduct of chlorine reacting with ammonia and nitrogen from organic contaminants. Chloramines are ineffective sanitizers and irritating to eyes and skin. Shocking the pool oxidizes and breaks apart chloramines, which eliminates the smell. If your pool smells strongly of chlorine, that is a sign it needs a shock treatment, not that it has been over-treated.
Can I swim right after I shock the pool?
No. Wait at least 24 hours after applying Cal Hypo shock before swimming. The label on Power Shock specifies a 24-hour waiting period. After 24 hours, test your free chlorine level. It should be between 1 and 3 ppm for safe swimming. If it is still elevated above 5 ppm, wait and retest.
Does the Power Shock raise cyanuric acid (stabilizer) levels?
No. Power Shock is a stabilizer-free formula (Calcium Hypochlorite). It will not raise your CYA levels. This is an important distinction from chlorine tablets (Trichlor) and some granular shock products (Dichlor), which add CYA with every dose. If your pool already has elevated CYA (above 80 ppm), switching to a Cal Hypo shock product like Power Shock prevents the problem from getting worse while still providing effective sanitization.
My pool turned green overnight after the storm. Is that algae or just cloudy water?
If it turned green within 12 to 24 hours of the storm, it is almost certainly an algae bloom that was triggered by the combination of warmth, sunlight, organic nutrients from runoff, and depleted chlorine. True algae turns the water green with a slightly slimy feel to the walls. Cloudy water from debris is typically gray or milky white rather than green. For a confirmed green pool, use the triple-dose treatment (3 lbs per 10,000 gallons) and brush the walls and floor thoroughly before and after applying shock.
How often should I shock my pool during storm season?
After every significant rain event, and once a week as a minimum during high-use summer months. A 24-count box of Power Shock contains enough for weekly maintenance of a 15,000 to 20,000 gallon pool for most of the swim season, plus additional doses for storm recovery. Shocking consistently prevents the kind of severe algae bloom that requires triple-dose treatment and days of recovery time.
Ready to Restore Your Pool?
The fastest path from green to clean is the right shock at the right dose, applied at the right time with the right chemistry foundation underneath it. Power Shock gives you a full season's supply of professional-grade 68% Cal Hypo in pre-measured bags, so every dose is accurate and every treatment is consistent.
