How to determine size of cartridge filter for pool

I have an approximately 20,000 gallon pool with a Hayward 1 1/2 HP pump. I have 2" pipe and approximately 50ft of head.

My current filter is a single cartridge with a stainless steel tank. I am unsure of the filters capacity, but it does not seem to be filtering my pool adequately.

The cartridge is only about 3 years old and appears to be in good shape. I would like to replace this with a new cartridge filtration, but I am unsure of what size filter to replace it with based on my gallonage and gpm.

Thanks for the question

It sounds like you're right in there with the pump motor size and plumbing. I've always heard, and it's worked for me through personal experience, that you want to have 100 - 200 sq. ft. more of filter per 10,000 gallons.

If you have a 10,000 gallon pool your cartridge filter sq. ft. would be 100 - 200.

20,000 gallons would be 300 - 400sq. ft.

30,000 gallons would be 400 - 500 sq. ft. and so on.

You always want a slightly larger filter. This way the system won't need to work as hard to filter. A smaller filter will have too much stress and pressure placed upon it. It won't filter as well and the life of the cartridge will be shorter.

Remember that it's the filter size and not necessarily the size of the pump motor. This is where pool owners get into trouble. They think that if a 1HP pump is good then a 2HP is twice as good. The water is flowing too fast and putting way too much pressure on the system.

Your 1.5HP pump motor should be fine for a 20,000 gallon pool.

For a 20,000 gallon pool, as stated above, I'd go with a cartridge filter that's 300 - 400 sq. ft.

I hope this has answered your question to your satisfaction.

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Hope this helps and have a great Summer.


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Operate And Vacuuming A Swimming Pool With A Cartidge Filter Lid Removed

by Anthony
(Alstonville, NSW Australia)

Question about swimming pool cartridge filter and vacuuming...

Our pool was only recently installed so the grass around has yet to grow back. A recent heavy downpour has seen a lot of mud in the pool.

The local pool shop has told us to use a solution to solidify the dirt particles. This should see them fall to the bottom of the pool to allow vacuuming.

We have been advised that when we vacuum we should take the lid off the swimming pool cartridge filter to reduce the amount of dirty water that goes back into the pool.

Is it O.K. to operate the cartridge filter with the lid removed?

Thanks for your question Anthony

I honestly have never heard that a pool owner can vacuum a pool with the cartridge filter lid removed.

This goes against everything I know about swimming pool pressure, vacuuming a pool, pressure, and have a closed loop of water from the pump motor through the plumbing and filter.

Swimming Pool Filter Cartridge..Care..Water Maintenance

Swimming Pool Vacuums..Cleaners..Care..Maintenance

Just because I've never heard of this before doesn't mean this can't happen, but I would ask your pool guy a few questions before doing this:

1. How exactly does this work?

2. Don't I need pressure and suction to vacuum?

3. If the lid is open won't that introduce air into the system?

4. If air gets into the system how will the pool build up enough pressure and suction to vacuum?

5. If enough air is in the system what will that do to my pool pump motor? Won't that reduce the amount of water that's in pump motor filter housing?

6. If there's not enough water and pressure in the pump won't that burn it up?

My understanding is a pool filtration system needs a "closed-loop" of pool water to operate correctly. The means water goes into the drains and skimmers, through the pipes and pool pump filter housing, through the filters, and is returned to the pool and clean water.

I think he might be saying to vacuum the pool with the cartridge filter lid off so the dirty water will just spray out into the yard.

If you can't vacuum your pool with the cartridge filter lid off, maybe your best bet is to buy a couple of replacement cartridges and have them on hand when the others become dirty.

Thanks for your question and I hope this clears some things up for you

All the best


Follow Up Comment:
By: Anthony

Operate And Vacuuming A Swimming Pool With A Cartridge Filter Lid Removed

Just thought I'd let you know. After some other attempts at cleaning the pool we bit the bullet and operated the cartridge filter with the lid off & it worked.

Made a mess with water going everywhere but looks like it's done the job we wanted.

Thanks for the reply Anthony

I knew the water would go everywhere but I honestly have never heard of this kind of thing working.

I guess you're never too old to learn something. The main thing is that your pool is cleared up and hopefully your pool cartridge filter is working properly.

If another pool owner has a question about this I'll be sure to direct them to this post.


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