Frequently Asked Questions
Twenty questions people actually search for, answered short, each linked to the page that answers it properly.
Questions people actually ask
How do I clear a green pool fast?
Test cyanuric acid and pH, brush every surface, shock to roughly 10 ppm free chlorine dosed by weight for your volume, then run the filter continuously until the water clears. Brushing first is the step people skip and the reason the shock underperforms. Full ordered fix: how to clear a green pool fast.
How much shock do I need for my pool?
For a 10 ppm shock: about 1.8 lb of 68% cal-hypo per 15,000 gallons, or 1.2 gallons of 12.5% liquid chlorine. The formula is lb = (ppm x gallons x 8.345) / (1,000,000 x available-chlorine fraction), and the dose tables for six pool sizes are on best pool shock.
Why is my pool green when the chlorine reading is fine?
Almost always cyanuric acid. Above roughly 50 ppm, stabilizer progressively blunts chlorine, so your reading is accurate and no longer tells you what the chlorine is doing. Test it before shocking a second time - see cyanuric acid.
My pool is green but there is no algae on the walls. What is it?
Probably dissolved metal - copper most often - rather than algae. Shocking a metals problem makes it worse, because chlorine oxidizes the metal and deepens the color. The bucket test on green water that is not algae tells you in a day.
Why is my pool cloudy after I shocked it?
Because the shock worked. Gray-cloudy water after a shock is dead algae in suspension, which is what a killed bloom looks like on the way out. Keep filtering, or use a flocculant to clear it overnight - cloudy after shock.
What is the difference between clarifier and flocculant?
A clarifier clumps particles until your filter can catch them, over 24 to 48 hours. A flocculant clumps them until they sink, so you vacuum them out overnight - which requires a multiport valve with a WASTE setting. Full comparison: clarifier vs flocculant.
How long does it take to clear cloudy pool water?
24 to 48 hours with a clean filter running continuously and the cause corrected. Overnight with a flocculant and a vacuum to waste. Past three days, the cause has not been fixed - only treated. See how to clear cloudy pool water fast.
What should my pool chemistry levels be?
Free chlorine 1 to 4 ppm for routine sanitizing, pH 7.2 to 7.6, total alkalinity 80 to 120 ppm, and cyanuric acid 30 to 50 ppm on a tablet pool or 60 to 80 ppm on a saltwater one. Those figures come from HTH's own product pages - the full table is on testing and chemistry.
What order do I add pool chemicals in?
Total alkalinity, then pH, then cyanuric acid, then chlorine. Alkalinity is the buffer that holds pH steady, so correcting pH first on a pool with low alkalinity means correcting it again within days. See how to balance pool water.
How much baking soda raises pool alkalinity?
About 1.4 lb of sodium bicarbonate raises total alkalinity by 10 ppm in 10,000 gallons - and that is a calculation, not a rule of thumb. The full derivation from molar masses is shown on how to balance pool water.
How do I lower my pool's alkalinity?
Add acid to bring pH to about 7.0 to 7.2, then aerate to raise pH back without raising alkalinity, and repeat. Acid lowers both readings; aeration raises only pH. It takes several cycles - how to lower alkalinity.
What is the best pool test kit?
Strips for the weekly test, because a kit that takes fifteen seconds actually gets used. Add a FAS-DPD titration kit if you shock regularly - color-match methods saturate above about 5 ppm chlorine, which is exactly the range that matters when shocking. See best pool test kits.
Do chlorine tablets raise cyanuric acid?
Yes, every trichlor tablet does as it dissolves. That is why a tablet-fed pool needs its cyanuric acid tested a few times a season - past about 50 ppm, more tablets make your chlorine progressively less effective. See best chlorine tablets.
How many chlorine tablets does my pool need?
HTH's published rate is one 3 inch tablet per 10,000 gallons per week, which it states holds free chlorine at 1 to 4 ppm. A 20,000-gallon pool therefore needs about two a week - roughly 48 over a 24-week season.
Will algaecide clear a green pool?
No. Algaecide prevents algae establishing; it does not remove an established bloom. Shock the pool, filter it clear, then dose algaecide to stop the next one - and not during the shock, because chlorine consumes it. See best pool algaecide.
Do leaves in a pool cause algae?
Not directly - they create both conditions algae needs. Decomposing leaves consume chlorine and release phosphate, which is algae food. HTH states that phosphate above 200 to 500 ppb makes algae harder to control. See do leaves cause algae.
Are robotic pool cleaners worth it?
If you vacuum more than weekly for several months a year, or your walls and waterline currently never get cleaned, yes. For a small above-ground pool that takes ten minutes to vacuum, no. The calculation is on are robotic pool cleaners worth it.
How much does a robotic pool cleaner cost to run?
About 39 kWh over a 24-week season at three three-hour cycles a week and 180 W - a few dollars at typical US rates. The electricity is not the cost; filters, brushes and eventually a battery are. Full arithmetic: what a robot costs to run.
How do I choose the right size robotic pool cleaner?
Work out your pool's total surface area including walls - length times width, plus twice the perimeter times average depth - and compare it against the coverage per cycle the maker publishes. A robot rated below your area stops partway through rather than cleaning slowly.
Have you tested the products you recommend?
No, and we say so on every commercial page. Units we claim to have tested: 0. What we do instead is compile the specifications each maker publishes, compute every dose from the percentage printed on the product, and cite the source next to the number. Our methodology sets out the whole method.