Filter Pressure
The gauge on the filter, read as a rise above whatever your own filter shows when it is clean.
- Measured in
- psi
No band, and none is implied. The trigger is a rise above your own filter's clean baseline, which is specific to your equipment and has nowhere in this product to live. Your filter's manual gives the figure it wants — for most, a rise of several psi over clean.
What it is
The pressure gauge reads how hard the pump is having to push water through the filter media. As the media loads up with dirt, the resistance goes up and so does the gauge. There is no universal correct pressure: it depends on the filter, the pump, the plumbing and how high the gauge sits above the water. The only number that means anything is your own filter's reading when it is freshly cleaned, and how far it has climbed since.
Why it matters
A blocked filter is a circulation problem, and circulation is what carries sanitiser around the pool and debris out of it. Pressure that has climbed and not been dealt with quietly undoes the chemistry — the readings at the skimmer stop describing the far end of the pool. Pressure that has fallen is the more urgent case, because it usually means water is not reaching the filter at all.
How to measure it
Read the gauge with the pump running and the air bled out, and read it at the same point in the cycle every time. The number is only useful next to your own clean baseline.
Your own equipment's display
- How trustworthy
- Ballpark
- Cost
- Free
- Effort
- None
The number your chlorinator, controller or filtration system shows you. Free and always there, and worth reading, but it is a sensor with a service life sitting in the water it is measuring.
The gauge on top of the filter. Bleed the air relief valve first — a filter with air trapped in it reads high for a reason that has nothing to do with the media.
Watch out: These gauges fail often, and they fail stuck. A reading that has not moved at all in months, through cleanings, is a gauge to replace rather than a filter to trust. They cost very little.
Where to find it: Already installed.
What you can see, taste and feel
- How trustworthy
- Ballpark
- Cost
- Free
- Effort
- None
Not a measurement, and it belongs here anyway: it is free, it is continuous, and it is what tells most people to test at all. Treat it as the prompt for a number, never as the number.
The returns tell you the same story before the gauge does: weakening flow, a surface that stops turning over, or a suction cleaner that has slowed to a crawl. Worth trusting when it disagrees with a gauge you have not replaced in years.
Where to find it: A clean, clear glass and a sheet of white paper.
Taking the sample
For several of these the sample is where the error is, and no instrument recovers from a bad one.
- • Always with the pump running and at operating speed. A variable-speed pump on its low setting reads lower for reasons that have nothing to do with the filter.
- • Take the clean baseline immediately after a backwash or a cartridge clean, and write it down. Without it every later reading is a number with nothing to compare it to.
If it is too low
Lower than it was usually means the pump is being starved rather than that the filter is especially clean: a blocked skimmer or pump basket, a low water level letting air in, a suction-side leak, or an impeller clogged with debris. Worth checking promptly, because running a pump dry damages it.
- • Check the skimmer and pump baskets first, then the water level, then the pump lid seal.
- • Look at the returns. Weak flow with low pressure points at the suction side; strong flow with low pressure usually means the gauge itself has failed.
- • Turn the pump off if it is running dry or making noise, and find the cause before turning it back on.
If it is too high
The media is loaded and flow is dropping. Everything downstream suffers — weaker returns, a pressure-side cleaner that slows down or stops, and a heater that may cut out on low flow.
- • Backwash a sand or DE filter, or take the cartridge out and hose it down.
- • If washing no longer brings it back to where it used to sit, the media needs a chemical clean — sunscreen and body oils blind a cartridge in a way water does not shift.
- • Record the new clean reading afterwards. That is the baseline everything after it is measured against, and a baseline that drifts up over years is how you know sand or a cartridge is due for replacement.
Common questions
What pressure should my filter be running at?
Whatever it read when it was last clean. There is no standard figure — filter size, pump, plumbing and the height of the gauge all move it, and two working pools can sit several psi apart. The question this parameter answers is how far it has climbed since, which is why no range is shown here.
How much of a rise means it is time to clean?
Your filter's manual gives the figure, and most name a rise of several psi over the clean reading. If you do not have the manual, the practical version is to clean it when the returns noticeably weaken and record what the gauge said, which gives you your own number for next time.
Why would I record this alongside water chemistry?
Because it explains chemistry that otherwise looks inexplicable. A pool that will not hold chlorine evenly, or that grows algae in one corner, is often a circulation problem rather than a dosing one — and the filter pressure logged that week is where that shows up.
WiseWaterGauge helps you record and understand your own readings. It is not a substitute for a certified laboratory test, and nothing here is medical or regulatory advice. If a health parameter is out of range, confirm it with an accredited lab and speak to your water provider.