Pool troubleshooter

Was it green when you took the cover off in spring?

• Yes, it opened green: Test cyanuric acid before you buy anything. It decides how much chlorine clearing the pool takes, and on a bad enough pool whether replacing water is the cheaper route. Test CYA before you buy anything, in Pool Opened Green? The Clear-Up, Start to Finish
• No, it turned during the season: next question

What does it look like?

• Green water, slippery walls: Green algae is the easiest to kill. It responds fast to proper chlorine levels. The kill, in How to Get Rid of Pool Algae (Green, Yellow, Black and Pink)
• Yellow dust on shaded walls that comes back after brushing: That’s mustard algae. It’s chlorine-tolerant and survives levels that wipe out green algae, so it needs the extra step. Mustard algae: the extra step everyone skips, in How to Get Rid of Pool Algae (Green, Yellow, Black and Pink)
• Dark raised spots in the plaster: Black algae has a protective layer and roots in the surface. It has to be broken open with a brush before chlorine does anything. The treatment, in Black Algae in a Pool: How to Kill It
• Pink or gray slime, or white growth like wet tissue: Neither is algae. Both often live in the plumbing, and they need very high chlorine held longer, plus attention to the plumbing itself. Pink slime and white water mold, in How to Get Rid of Pool Algae (Green, Yellow, Black and Pink)

Did it come up cloudy right after opening for the season?

• Yes, right after opening: Spring cloudiness is usually winter debris, dead algae and a filter that sat dry, all at once. The order of the fix matters, and clarifier comes last. The special case: cloudy after opening, in Cloudy Pool Water: Causes and How to Clear It Fast
• No: next question

Is free chlorine at least 11% of your CYA reading?

At 40 ppm CYA that’s about 4.4 ppm free chlorine.

• No, it’s lower: Chlorine too weak for your stabilizer is the most likely cause, and cloudy is often the warning before algae. Bring chlorine up and give it 24 hours. Work through it in this order, in Cloudy Pool Water: Causes and How to Clear It Fast
• Yes, it’s at or above that: next question
• I haven’t tested yet: Test first. The guide works through the causes cheapest and most likely first, starting with chlorine against your CYA. Work through it in this order, in Cloudy Pool Water: Causes and How to Clear It Fast

Is filter pressure 8 psi or more above its clean reading?

• Yes: The filter is restricting flow, and that alone leaves water hazy. Clean it and note the clean pressure for next time. How to Clean a Pool Filter (Sand, Cartridge and DE)
• No, or I don’t know the clean reading: Work down the remaining causes. If you have no clean reading, clean the filter, note the pressure and start keeping one. The six causes, and what each one actually needs, in Cloudy Pool Water: Causes and How to Clear It Fast

What’s your cyanuric acid (stabilizer) reading?

• Below 20 ppm, on an outdoor pool: Sunlight is burning it off. That’s the answer, and the fix is stabilizer rather than a diagnosis. First, rule out sunlight, in Pool Won't Hold Chlorine? Work Out Which Demand You Have
• 20 ppm or more: next question
• High, and algae grows even with chlorine showing: High CYA locks chlorine up, so algae grows while the reading looks fine. That needs dilution rather than more chlorine. First, rule out sunlight, in Pool Won't Hold Chlorine? Work Out Which Demand You Have
• I don’t know: Test CYA before anything else. A pool with little or none loses most of its chlorine across a sunny afternoon. First, rule out sunlight, in Pool Won't Hold Chlorine? Work Out Which Demand You Have

How much free chlorine did you lose overnight?

Test at dusk once the sun is off the water, then again at dawn before it returns. Same drop kit both times.

• Under 1 ppm: That’s normal loss. The chlorine may never have been gone: a stale test kit or metals in the water are the next checks. Two answers that are not demand at all, in Pool Won't Hold Chlorine? Work Out Which Demand You Have
• 1 to 3 ppm: Real organic demand, usually early algae, often somewhere you haven’t looked. Organic demand, in Pool Won't Hold Chlorine? Work Out Which Demand You Have
• More than 3 ppm, or all of it: A serious demand. The guide works through organic demand first, then ammonia, which behaves differently. Organic demand, in Pool Won't Hold Chlorine? Work Out Which Demand You Have
• I haven’t run the test: Run it tonight. With the sun removed, what is left is consumption by things in the water, which is the number you want. The overnight loss test, in Pool Won't Hold Chlorine? Work Out Which Demand You Have

Which of these is it doing?

• Never primes: it churns air and water never arrives: Usually a bigger air leak, a blockage or no water available at the skimmer. Start with the water level. Work through it, in Pool Pump Won't Prime? Work Through It in This Order
• Primes, then loses it after 5 to 30 minutes: Almost always a small air leak that builds up over time, a water level that drops during the run, or a filter clogging as it runs. Work through it, in Pool Pump Won't Prime? Work Through It in This Order
• Primes, but the flow is weak: That’s restriction, not prime loss, and a different guide. Low Pool Water Pressure: What Causes It and How to Fix It

What does it do when it should be running?

• Nothing at all: no hum, no sound: next question
• It hums, but the shaft never turns: Power is reaching the motor and it can’t turn. With the breaker off, turning the shaft by hand tells you whether it’s jammed or electrical. It hums but won't spin, in Pool Pump Won't Turn On? Silent, Humming or Tripping
• It trips the breaker or the GFCI: Two different warnings. A GFCI that trips by itself means current is reaching ground, and the pump stays off until an electrician finds it. It trips the breaker or the GFCI, in Pool Pump Won't Turn On? Silent, Humming or Tripping
• It runs, then shuts itself off: The motor is overheating and protecting itself. Airflow around the motor, then the voltage, are the first things to check. It runs, then shuts itself off, in Pool Pump Won't Turn On? Silent, Humming or Tripping
• Its keypad is flashing or showing a code: The drive has stopped on a fault. Read the code before you reset it, because it says where to look. Variable-speed pumps: read the light first, in Pool Pump Won't Turn On? Silent, Humming or Tripping

Is it a variable-speed pump with its keypad lit?

Look at the buttons or display on the pump itself, not the timer or the automation panel.

• Yes, the keypad is lit: It has power, so it has been stopped or is waiting for its next schedule. A pump stopped from its own keypad stays stopped until someone restarts it. It's silent, in Pool Pump Won't Turn On? Silent, Humming or Tripping
• No, or it’s a single-speed pump: Nothing is telling it to run, or no power is reaching it. Check the timer or schedule first, then the breaker and the GFCI. It's silent, in Pool Pump Won't Turn On? Silent, Humming or Tripping

Is it a gas heater or a heat pump?

• Gas heater: next question
• Heat pump: next question

Does it never light, or light and then shut off?

• It never lights: Flow is the most common cause by a distance: a dirty filter, a pump speed below the heater’s minimum, or a partly closed valve. 1. Flow, in Pool Heater Not Heating? Diagnose It in Order
• It lights, then shuts off within minutes: A much shorter list than a heater that never lights: flow that’s fine at ignition but not under load, or gas supply that can’t sustain the draw. When it fires and then stops, in Pool Heater Not Heating? Diagnose It in Order

Does it not run at all, or run and fall behind in cool weather?

• It doesn’t run at all: Check flow first. It’s the most common cause by a distance. 1. Flow, in Pool Heater Not Heating? Diagnose It in Order
• It runs, but heats slowly or stops when it’s cool: Output falls as the air cools, and around 50°F the coil has to defrost, which stops heating while it runs. None of that’s a fault. Heat pump specifics, in Pool Heater Not Heating? Diagnose It in Order

Test free chlorine with a kit, not the panel. What do you find?

The panel reports what the cell is doing, not what is in the water.

• Zero, and the panel says it’s working: A production problem. Check flow and the other basics before you pull the cell. The four things to check before touching the cell, in Salt Cell Not Producing Chlorine? Check These Four Things First
• Low but not zero, and the panel says it’s working: Usually demand or arithmetic rather than a fault. Output percentage is a duty cycle, and it multiplies with pump hours. Chlorine is low but the cell says it is generating, in Salt Cell Not Producing Chlorine? Check These Four Things First
• The panel shows a no-flow or other warning: A no-flow condition and a dead cell look identical. Check that water is actually moving through the cell first. The four things to check before touching the cell, in Salt Cell Not Producing Chlorine? Check These Four Things First

Have you run a bucket test yet?

A weighted bucket on a step, filled to match the pool, both levels marked, compared after 24 hours.

• Not yet: It tells evaporation from a leak for the price of a bucket. A quarter to half an inch a day is ordinary in hot, dry, windy weather. Doing it properly, in The Pool Bucket Test: How to Prove You Have a Leak
• Yes, and both dropped the same: No leak. The water is evaporating, and a cover is the lever. What to do with the answer, in The Pool Bucket Test: How to Prove You Have a Leak
• Yes, and the pool dropped more: next question
• Yes, but I am not sure how to read it: Step 6 says how to read the marks, and the bucket test calculator right after the steps does the arithmetic: leak or not, and how many gallons a day. Doing it properly, in The Pool Bucket Test: How to Prove You Have a Leak

How did the pool lose the water?

Run the test once with the pump on and once with it off.

• More with the pump running: Pressure-side plumbing. Start at the equipment pad, where a wet patch or a weeping union is free to find and cheap to fix. What to do with the answer, in The Pool Bucket Test: How to Prove You Have a Leak
• About the same, pump on or off: The shell or a fitting. Dye testing is the next step. Dye testing the shell, in How to Find a Pool Leak (Before You Pay Someone to Dig)
• It dropped to one level and stopped: The leak is at the level where it stopped, most often the skimmer throat, a return fitting or the tile line. Reading the pump-on against the pump-off run, in The Pool Bucket Test: How to Prove You Have a Leak

Did you clean the filter, empty the pump basket or backwash in the last few minutes?

• Yes, just now: Air gets in whenever the system is opened. Give it fifteen minutes of steady running; if the bubbles thin out and stop, nothing is wrong. First, rule out normal, in Air Bubbles From Your Pool Returns: Find Where Air Gets In
• No, or it’s still bubbling after 15 minutes: next question

Look through the clear pump lid while it runs. What do you see?

• Full of water, with occasional bubbles at the jets: A small leak, most likely the lid o-ring or a plug. What the pump basket tells you, in Air Bubbles From Your Pool Returns: Find Where Air Gets In
• A third to half full of air: A real leak, worth shutting off for. Work along the suction side from the skimmer to the pump. Work along the suction line, in Air Bubbles From Your Pool Returns: Find Where Air Gets In
• Full of water, but pressure and flow are low: Probably not an air leak at all. That’s restriction, and a different guide. Low Pool Water Pressure: What Causes It and How to Fix It