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I'm trying to determine how long I actually have to run my pool filter per day, but my maths are not adding up. Most places on the internet (that I've come across), recommend 8-12 hours per day. The maths I've done, says ~4 hours per day. Why is there such a large discrepancy?

I've calculated that the pool capacity is somewhere around 11,227 gallons.

Volume = pi*r*r*h
V = pi * 126" * 126" * 52"
V = pi * 15876 * 52"
V = pi * 825552 V = 2593548.0983563609875993121703532 cu.in.

1 cu.in = 0.004329 US gal.

Gallons = 2593548.0983563609875993121703532 * 0.004329
gal. = 11,227.469717784686715317422385459

The documentation that came with the filter lists a Design Flow Rate of 100 gallons per minute (GPM), and an 8 hour turnover of 48,000 gallons.

enter image description here
Hayward XStream® Filtration

Based on all this, it seems that if I run the filter for 8 hours, I'll have turned the water over more than 4 times. Is this really the case? Could I run the filter for only 4 hours a day, and still meet the recommended 2 turns per day?

Using 100 GPM rate, and the capacity of the pool. I've calculated a running time of just under 4 hours.

11,227.5 gallons x 2 turns = 22,455 gallons per day
22,455 gallons / 100 GPM = 224.55 minutes
224.55 minutes / 60 minutes = 3.7425 hours

I'll have to check to be sure, but I think the pump I have is the Hayward Power-Flo® LX (SP1580X15).

The gauge on the filter reads ~14 PSI, so...

Head (feet) = PSI * 2.31
Head = 14 * 2.31
Head = 32.34

Based on this chart, I should actually be somewhere around 80 GPM.

enter image description here

80 GPM

22,455 gallons / 80 GPM = 280.6875 minutes
280.6875 minutes / 60 minutes = 4.678125 hours

70 GPM

22,455 gallons / 70 GPM = 320.78571428571428571428571428571 minutes
320.78571428571428571428571428571 / 60 minutes = 5.346 hours

60 GPM

22,455 gallons / 60 GPM = 374.25
374.25 / 60 minutes = 6.2375 hours


Bonus:

Is it better to do the 2 turns at once (run 8 hours straight), or split it up (run twice for 4 hours each time)?

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Based on a discussion I had with my pool tech a couple years ago, that 90 GPM rating on the pump is measured with nothing hooked up to it causing back-pressure. So it may push 90 GPM with nothing attached, but the filter and all the pipes are going to slow it down, possibly as much as 50%. –  longneck May 12 at 13:37
    
@longneck From what little I know about this pump, it seems the pump is rated at 100 (or 120 not sure) GPM, but with the filter and plumbing should be around 80-90 GPM. I guess I could measure it for the most accurate measurement, but I'm trying to get a better understanding of the whole situation. –  Tester101 May 12 at 13:42
    
Wow you've done far more calculation than I have on this. However I can say your pool is close to the size of mine and I run mine for generally 10-12hrs a day depending on factors like usage, how much it's rained, etc. Your hayward is a good brand, but...if you under-calculate you'll end up with a green pool in no time. I've also been told it depends whether it's saltwater or chlorine etc should add as an additional factor. Advice I was always given, don't try to be overly cheap as it will cost more in the long run. Not an answer but hopefully helpful. –  Chris W. May 12 at 18:35
    
Think about this, I have a in ground hot tub with pool equipment for filtering/heating. I get a turn over in 45 minutes but 4 hours each day wasn't enough to keep pink slim from forming. Once I bumped my time to 6 hours each day the problem whet away. Getting the required turn overs is needed but if the water sits too long between turn overs it just as bad. Experiment and find out what works for your poll. –  diceless May 13 at 5:00
    
@diceless That's why I was thinking of splitting up the running time. I want to run half the time in the morning, and the other half in the evening. This way I get the proper turn over, and the water doesn't sit stagnant too long. –  Tester101 May 13 at 12:20

1 Answer 1

This is more of a comment but too long...

I was a pool boy through college. I have also owned 3 pools. What you are doing has too many variables. You have temperature, environment, chlorine levels, quality of original water, amount of swimmers, pump size, plumbing size, pool depth, almost anything around the pool is a variable.

So as a kid I would clean pools, add chemicals and often people had me set up their timers. But I was a dumb kid and was told 12 hours minimum and 16 hours for bigger pools. Usually in 2 shifts a day and we tried to set up timer to hours they were not swimming.

Some customers though set up their own timers and the times were literally all over the place. I have seen oversized pumps on for 2 x 2 hour shifts and the pool never had an issue (pool was in the middle of a yard not close to house, trees, and wasn't swam in a ton). I have seen algae grow in a pool that was being pumped 12 hours a day.

I would think that for your size pool and pump your baseline is 2 x 4 hours. I would consider 3 x 2.5 hours too. From there you can work your way down or up as needed. The big thing is if you are playing with the filter times then you need to keep an eye on the pool. You have to figure that each hour a day might be $8-15 a month in electric costs. But at the same time will you have to spend a ton of money on chemicals to fight an algae problem and all the time that goes with that.

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