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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

2 Answers 2

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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The Calculations which I have done (metric conversion) indicate that your water flows through your filter about 1.8 times per hour. but i will address that later.

Firstly. the reason(s) why your pump needs to run for certain durations will be dependant on a few factors - which need to be managed/considered before you do your calculations

  • Water filtration time: "For sufficient filtering, the entire body of water should flow through the filter at least twice in a 24 hour period" source
  • Cleaning of pool Wall Surface - your pool cleaner needs time to be able to cover the entire surface of the pool, if you do not clean the sides of the pool, it will develop algae on the surface, and get dirty sooner
  • Direct or indirect sunlight - the filtration time changes from summer to winter (almost by half the requirement in winter) Direct sunlight will convert chlorine to the needed "free radicals" faster and consume more chlorine hence Its a good idea to supplement your pool with Stabilizer in the summer (cyanuric acid)
  • Chlorinator present? - If you have a chlorinator fitted. then your pool chlorine levels will be more consistent enabling you to more accurately limit the time needed to run the filter. however the chlorinator needs to have water running through it in order to create the chlorine this will affect your run time.
  • Filter size and quality of sand - (2bag, 3bag and 4bag) filters typically will require larger motors, and will filter more water.
  • Human intervention - How often do you sweep the pool sides, and change the basket, these will need to be done more frequently the less you run your pool.
  • Water PH levels - maintained levels at 7.2 to 7.6ph are ideal.. also other chemicals should be:
    • Free chlorine: 0.5-1.5 ppm (mg/l)
    • Combined chlorine: 0-0.5 ppm (mg/l)
    • Total chlorine: 0.5-1.5 ppm (mg/l)
    • Cyanuric acid: 0-20 ppm (mg/l)
  • Pool Skimmer - If you have a pool skimmer installed, it will be more effective to remove floating debris. hence the need to filter the pool will be reduced. Decomposing leaves are a great breeding ground for algae!
  • Pool Cover and temperature - Pool cover will require less cleaning time, and less filtration time. however increased temperature will improve the climate for bacteria.
  • Pool pump effectiveness - recorded flow rate of the pump is affected by the length of pipe from pump to pool. quality of sand, size of filter and relative height of pump.
  • Running the pool day or night - Some people prefer to run the pump at certain times of the day. what is true is that sunlight is needed to make the chlorine effective (too much is also not good) and the moving water may heat up sooner in daylight. also a loud pump is better running at night for the neighbours... algae grows in sunlight, so its better in the day.
  • Frequent pump startups - in my opinion, pool motor bearings take strain if they are started and stopped to frequently. The motor and bearings heat up and expand.. this action will shorten the lifespan of the motor (so run for at least two hours at a time)

so basically, the motor filtration rate is only one factor in many. You need to manage all the variables and this will enable you to run the pump as little as possible. a basic indication of times is given below

enter image description here

Any time that have your motor off you are allowing algae levels to build up, essentially the filter is stopping the rate of excessive exponential growth. and at low levels, the chlorine is sufficent you dont want the algae levels too high at any time for this, I would recommend that you have your pump run twice a day.

So to answer your question. For now, I would run your pump for an hour in the morning (say 9am) then for two hours in the late afternoon (say 3-5pm) in the Summer then for winter i would go as crazy as to say that you run your pump once every 2 days for 3 hours. There is no exact science to this (too many variables) if you see the water starting to turn. check the levels then add 30mins to the filtration time.

You will be surprised how little the pump needs to be on provided that you constanly maintain the correct conditions for your pool.

share|improve this answer
    
I don't have a sand filter, does the table still apply? –  Tester101 Jun 25 at 10:00
    
I am not too familiar with the other types (cartridge and DE filters). cant help there. Sorry. –  Hightower Jun 25 at 19:45

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