\n| Dark green\/black<\/td>\n | 30 ppm<\/td>\n | 6 lbs calcium hypochlorite<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n Important:<\/strong> Always shock at dusk or night. Sunlight destroys chlorine at 1 ppm per hour. Shocking at noon wastes half your chemical before it even starts working.<\/p>\nBroadcast the shock around the pool perimeter with the pump running. Don’t pour it all in one spot \u2014 you’ll bleach your liner or plaster.<\/p>\n Step 5: Run Your Filter 24\/7<\/h3>\nYour filter needs to run continuously until the water clears. We’re talking 24 hours a day, minimum 48-72 hours straight. Yes, your electric bill will notice. It’s still cheaper than draining and refilling.<\/p>\n The filtration process:
\n1. Hours 1-12:<\/strong> Water stays green, dead algae circulates
\n2. Hours 12-24:<\/strong> Water turns cloudy gray\/white (good sign!)
\n3. Hours 24-48:<\/strong> Water begins clearing, cloudiness fades
\n4. Hours 48-72:<\/strong> Crystal clear water returns<\/p>\nStep 6: Backwash or Clean Filter Every 8-12 Hours<\/h3>\nThis is crucial and often forgotten. Your filter is catching millions of dead algae cells. When it clogs, water bypasses the filter media entirely, and all that dead algae recirculates.<\/p>\n \n- Sand filter:<\/strong> Backwash for 3 minutes when pressure rises 8-10 PSI above clean baseline<\/li>\n
- DE filter:<\/strong> Backwash and add fresh DE<\/li>\n
- Cartridge filter:<\/strong> Remove and hose down thoroughly (have a spare cartridge so you can swap without downtime)<\/li>\n<\/ul>\n
You might backwash 3-4 times over 48 hours. That’s normal for a heavy algae kill.<\/p>\n Step 7: Retest and Maintain Shock Level<\/h3>\nHere’s the key most people miss: test chlorine every 4-6 hours and re-shock as needed. The algae kill isn’t complete until you achieve OCLT \u2014 Overnight Chlorine Loss Test.<\/p>\n Run the OCLT after water looks clear:
\n1. Test chlorine at sunset (after brush and backwash)
\n2. Test again at sunrise (before sun hits pool)
\n3. If you lost more than 1 ppm overnight, algae is still present<\/p>\n Keep shocking until chlorine loss is under 1 ppm overnight. Only then is it safe to return to normal chlorine maintenance.<\/p>\n Preventing Green Pool Disasters<\/h2>\nFixing a green pool costs time, money, and sanity. Prevention costs five minutes a day.<\/p>\n Test Three Times Per Week Minimum<\/h3>\nQuick 30-second dip strip tests between major testing sessions. You’re looking for chlorine below 1 ppm \u2014 that’s your algae warning sign. Catch it at 0.8 ppm and you can fix it with minor shocking. Wait until 0.2 ppm and you’re fighting a bloom.<\/p>\n Maintain Proper Chlorine Levels<\/h3>\nThe magic number is 7.5% of your CYA level. If CYA is 40 ppm, you need minimum 3 ppm free chlorine at all times. If CYA is 50 ppm, target 4 ppm chlorine.<\/p>\n This ratio keeps chlorine effective against algae growth. Most “my pool is always green” problems come from chronic low chlorine.<\/p>\n Weekly Shocking<\/h3>\nEven when water looks perfect, shock weekly during swim season. This oxidizes organic contamination before it becomes food for algae. Use 1 lb of shock per 10,000 gallons every 7 days as preventative maintenance.<\/p>\n Clean Your Filter Regularly<\/h3>\nA dirty filter doesn’t just slow circulation \u2014 it becomes a bacterial breeding ground. Clean cartridge filters every 2-4 weeks, backwash sand\/DE filters when pressure rises 8-10 PSI.<\/p>\n Address Phosphates<\/h3>\nPhosphates are algae fertilizer. They enter your pool from:
\n– Lawn runoff (fertilizers)
\n– Dead leaves and debris
\n– Some municipal water supplies
\n– Certain algaecides<\/p>\n Test phosphates twice per season. If above 300 ppb, use a phosphate remover before algae gets a foothold.<\/p>\n When to Call a Professional<\/h2>\nDIY pool recovery works 90% of the time. But some situations need expert help:<\/p>\n \n- Black algae:<\/strong> This stubborn variant has deep roots in plaster\/concrete. Standard shocking rarely kills it completely. You may need acid washing or professional treatment.<\/li>\n
- Mustard algae:<\/strong> Chlorine-resistant and requires specialized algaecide combined with equipment cleaning (including toys, floats, and vacuums).<\/li>\n
- Repeated failures:<\/strong> If you’ve shocked three times and water won’t clear, something else is wrong \u2014 possibly equipment failure, high CYA, or contaminated fill water.<\/li>\n
- Equipment damage:<\/strong> Green water sitting for weeks can damage pump seals, corrode heater elements, and stain pool surfaces. A professional can assess damage.<\/li>\n<\/ul>\n
Pool service runs $150-300 for algae treatment. Compare that to the $80+ in chemicals and 10+ hours you’ll spend doing it yourself. Sometimes the professional is worth it.<\/p>\n Calculating Your Chemical Needs<\/h2>\nHere’s where guessing fails and math wins. A 20,000-gallon pool needs exactly twice the chemicals of a 10,000-gallon pool. Eyeballing it leads to under-shocking (algae survives) or over-shocking (wasted money, potential damage).<\/p>\n To get exact measurements for your pool, head to Pool Calculator<\/a>. Enter your pool volume and current chemical levels, and it’ll tell you precisely how much shock, acid, or other chemicals to add. Takes 60 seconds and eliminates the guesswork that causes most algae treatment failures.<\/p>\n
\nFrequently Asked Questions<\/h2>\nIs it safe to swim in a green pool?<\/h3>\nNo. Green pool water contains millions of bacteria and potentially harmful pathogens that thrive alongside algae. Beyond health risks, you simply can’t see the bottom \u2014 creating a drowning hazard. Wait until chlorine drops below 5 ppm and water is crystal clear before swimming.<\/p>\n How long does it take to clear a green pool?<\/h3>\nMost green pools clear in 24-72 hours with aggressive treatment. Light green (still see bottom) often clears within 24 hours. Dark green or black-green pools may take 5-7 days of continuous treatment. The biggest variable is your starting chlorine level and whether CYA levels are in check.<\/p>\n Can I use algaecide instead of shocking?<\/h3>\nAlgaecide alone won’t clear a green pool. It’s designed to prevent algae, not kill active blooms. Think of algaecide as the defensive line and chlorine shock as the offense. You need shock to kill the existing algae, then algaecide to prevent regrowth. Using algaecide first actually coats algae cells, making them harder for chlorine to penetrate.<\/p>\n Why does my pool keep turning green even though I add chlorine?<\/h3>\nThe most likely culprit is high cyanuric acid (CYA). Test your CYA level \u2014 if it’s above 70-80 ppm, chlorine becomes ineffective regardless of concentration. The solution is partial draining (30-50% of pool volume) and refilling with fresh water to dilute CYA. This is the #1 cause of chronic green pools in homes using stabilized chlorine tablets.<\/p>\n How much does it cost to fix a green pool?<\/h3>\nBudget $50-150 in chemicals for a DIY fix (10,000-20,000 gallon pool). This includes 4-6 lbs of shock ($25-40), pH adjusters ($10-15), algaecide for prevention ($15-25), and filter cleaner ($10-15). Professional treatment runs $150-300. The real cost is time \u2014 expect 4-8 hours of active work spread over 2-3 days.<\/p>\n Need help calculating the right shock dose before your green pool gets worse?<\/strong> Use Pool Chemical Calculator<\/strong> to calculate chlorine, shock, pH, alkalinity, stabilizer, calcium hardness, salt, and more from your exact pool volume and current test results. No guessing, no wasting chemicals, no \u201cdump and pray.\u201d<\/p>\n???? iPhone \/ iPad:<\/strong> https:\/\/itunes.apple.com\/us\/app\/pool-chem-calculator\/id1453351222
\n???? Android:<\/strong> https:\/\/play.google.com\/store\/apps\/details?id=com.poolchemicalcalculator.poolcalc
\n???? Full guide:<\/strong> https:\/\/poolchemicalcalculator.com\/news\/pool-water-turns-green-overnight\/<\/p>\n
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