Filtration. What you may have overlooked.

Although proper filtration is an integral part in maintaining water clarity, that isn’t necessarily determined by your filter. It is actually determined by 3 words: GPM (Gallons per minute). Now before you say anything let me explain…

The whole emphasis behind truly healthy swimming pool water is circulation. For instance if you have perfectly balanced pool water but the water is also stagnant, it will eventually start to lose its color regardless of how many chemicals you put in.

For this reason filtration becomes essential but is still second behind circulation. In other words the amount of filtration that takes place in your pool is solely dependent upon how much water you’re moving. And the more water you filter the better. Also the amount of water your moving depends on…Yup, you guessed it, the size of your motor.

So how do you determine if you’re properly circulating your swimming pool water? Ask your pool technician… Just kidding, ill tell you. Basically the ultimate goal in circulating and filtering your water is to turn over you pool water at least once in 8 hours. (Not including variable speed motors or 2-speed motors) In a perfect world it would be twice.

Now lets get to work.

  • First you need to figure out how many gallons of water your pool is. This should help.
  • Then divide the number of gallons by 8, which gives you GPH (Gallons per hour).
  • Next take that number (GPH) and divide by 60, which gives you GPM (Gallons per minute).

For example, if you have a 20,000 Gallon pool:

GPH = 20,000 / 8 = 2,500

GPM = 2,500 / 60 = 41.7

Now if you wanted to get really technical you would need to determine the Pump Output (GPM) vs. Total Resistance To Flow (Feet of Head). Which is basically the pumps distance from the pool factored in but for this topics sake lets not get too technical.  Its not like we’re building a pool over here. Relax! Plus your pool builder should handle all that. You get the idea…#KeepItSimpleStupid

So once you’ve determined your GPM you’ll know exactly what size motor you need to properly circulate your water. A majority of the motors should have a chart on them to go by but you can always ask your pool professional.

Ok, now we can talk about your filter. Finally…and really your filter just needs to match the size of your motor. Filters have a designed flow rate also in GPM, which should just be a little higher than your motors output.

That being said, the reason filter size is so important to the amount of water you will be moving instead of just pool size is because each filter has a different size filtration area. For example a 120 sq. ft. cartridge filter has a filtration area of 10 ft. x 20 ft. In other words if you actually unraveled your cartridge filter it would span and cover that area of 10 ft. x 20 ft.

Kind of like this: (80 sq. ft. – 8 ft x 10 ft.) in actual pic.

filter area 80ft








Proper filtration area is important to ensure that once your circulating the right amount of water you are also filtering the right amount.

So then why not just purchase the biggest filter possible and save yourself a headache and stop reading right now? Because (and myth busted) bigger isn’t always better. The entire reason your filter is directly related to your motor in the first place is because of the simple fact of how filters physically work…Pressure.

Water is physically forced through filters sand, cartridge, or grids (obviously depending on which type of filter you have) trapping any debris caught in its path. So too big of a filter will ultimately result in lack of pressure essentially creating water just swirling around in a bucket. And too small a filter will obviously create too much pressure running the risk of plumbing leaks, hairline cracks, or damage to the cartridge itself.


So without the proper amount of pressure you are unable to properly filter you pool water. So remember: Circulation first. Filtration a close second!


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