Pool care guides
The question people ask most after shocking a pool is when it is safe to get back in, and the answer is a reading of 4 ppm rather than a number of hours.
These guides cover the questions a calculator alone cannot answer — the ones about timing, side effects and what to do when the obvious fix has not worked. Each one ends in a number you can act on, and carries the calculator that produces it.
How long after shocking can you swim?
Test for 4 ppm rather than counting hours, and why the usual answer misleads.
Can you over-shock a pool?
The chlorine is not the problem. What dichlor and cal-hypo leave behind is.
How many bags of shock does my pool need?
What double, triple and quadruple shock really track, and how to count bags for your pool.
Why is my pool still green after shocking?
The dose was too small, too short, or the green is metal rather than algae.
How do you lower CYA in a pool?
Draining is the only fix that works. How much, and why one big drain beats several small ones.
How much chlorine do you need to open a pool?
Clear water needs a normal dose and an overnight test. Green water needs the shock level for your CYA.
How do you raise pool alkalinity without raising pH?
Baking soda, not soda ash: how much to add, and how to handle the small pH rise.
How much does it cost to run a pool pump?
Watts, hours and your rate: the monthly bill, and the two changes that cut it most.
How often should you shock a pool?
Shock on a test result, not a calendar: the three readings to watch, and the routine dose.
Start with your volume
Every dose on this site scales with how much water you have, and most people are working from a number the previous owner guessed at. Measure it once with the pool volume calculator and write it somewhere you will find it again. If yours is a standard shape, the pool sizes pages list the gallons for common round, oval and rectangular pools at three depths.
Then the three readings that matter
Free chlorine, pH and stabilizer explain most pool problems between them. Chlorine that vanishes overnight usually means algae rather than a bad batch of product. Chlorine that tests fine while the water stays dull usually means stabilizer has climbed high enough to hold it inactive, which the CYA calculator will tell you. Cloudy water after a correct dose is often calcium or alkalinity, not sanitizer at all — the water balance calculator sorts that out in one reading. Fix the cause and the chlorine looks after itself.