Become a TFP Supporter Pool Math Forum Rules Pool School
Results 1 to 15 of 15

Thread: Backwashing every three days - what's wrong?

  1. Back To Top    #1

    Backwashing every three days - what's wrong?

    This is an IG pool with a sand filter, used by homeowners in a residential subdivision (I'm the new HOA president). 30' x 50' and approx. 39,000 gallons.

    The filter and sand are new this year.

    After we backwash, the pressure drops to 18 PSI and stays there for about 3 days. By the fourth day, it has spiked to 30+ PSI, flow slows and we backwash. I know this isn't right and the pool service tech seems as puzzled as I am.

    Skimmers and strainer are cleaned regularly.

    Any ideas?
    Mike Bowers
    Georgia, 44,000 gallon, in ground, salt water, gunnite

  2. Back To Top    #2

    In the Industry

    duraleigh's Avatar
    Join Date
    Apr 2007
    Location
    Sebring, Florida
    Posts
    30,083

    Re: Backwashing every three days - what's wrong?

    Yes. Your filter is filtering debris (most likely dead algae) from the water....as it is supposed to do.

    You almost surely need to shock the pool. Posting a full set of test results is the first step.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

  3. Back To Top    #3
    Mod Squad zea3's Avatar
    Join Date
    Jul 2009
    Location
    Houston, Texas
    Posts
    9,200

    Re: Backwashing every three days - what's wrong?

    How does the water look? Is it cloudy? You are probably on the verge of an algae bloom. Post a complete set of current test results and perform an overnight free chlorine loss test to see if you need to begin the shock process.
    TFP Moderator
    Helpful links: TF Test Kits,TFP Pool School, PoolMath
    Vogue 21' round AG, Pentair 1 hp 2 speed pump, 36 sq ft DE filter, Hayward S180T 150# sand filter, Houston, Texas
    Love TFP? Become a
    TFP Supporter!

  4. Back To Top    #4
    Mod Squad JohnT's Avatar
    Join Date
    Apr 2007
    Location
    SW Indiana
    Posts
    9,089

    Re: Backwashing every three days - what's wrong?

    What size is the filter?
    TFP Moderator
    20K Gallon 20X36 Vinyl Inground
    Hayward S244T Sand Filter with 1HP Whisperflo Pump. Liquidator C-201 and Solar Heat

  5. Back To Top    #5

    Re: Backwashing every three days - what's wrong?

    It's a Pentair Triton C, TRC 140, 36" Heavy Duty Commercial sand filter.

    We have been having trouble keeping the free chlorine level in the proper range. I'll get the readings and post them later today.

    Thanks.
    Mike Bowers
    Georgia, 44,000 gallon, in ground, salt water, gunnite

  6. Back To Top    #6

    Join Date
    Jun 2012
    Location
    Minneapolis, MN
    Posts
    16

    Re: Backwashing every three days - what's wrong?

    If it helps any, I take care of the pool for a large townhome community, so I know it can be frustrating to deal with. I don't know about you, but today the high here is supposed to be 100 with about a 75 dew point, so we get HEAVY bather loads every day. Right now, I am not having ANY problems, and that's to the credit of the wonderful folks here.

    So, I am by no means an expert, but yes, especially if you're having trouble holding FC levels, it's most likely time to shock. Do you know what your CC level is (measured by doing the FC and TC tests and subtracting to get the difference)? I am finding I have to shock our pool at least every other week, but when we have a hot streak where it's 95-100 every day, I have to do it weekly. And I end up backwashing a lot more.

    Keep us posted and we'll help you!
    27,000-gallon plaster IG, sand filter, flow rate 80-90.

  7. Back To Top    #7

    Re: Backwashing every three days - what's wrong?

    It's a salt water system. One meter reads 3000 and the other is 2800. I'm told this is the bottom end of acceptable. The system indicates that it is generating chlorine. No warning lights.

    Readings this morning: Chlorine: 3; pH: 7.6; Alk: 90.

    The water looks a little cloudy.

    I'll see if I can find the TC level. I haven't seen that on the daily report.

    This is especially frustrating since we pay a pool service to take care of this stuff for us.
    Mike Bowers
    Georgia, 44,000 gallon, in ground, salt water, gunnite

  8. Back To Top    #8

    In the Industry

    duraleigh's Avatar
    Join Date
    Apr 2007
    Location
    Sebring, Florida
    Posts
    30,083

    Re: Backwashing every three days - what's wrong?

    Post up CH and, especially, CYA....that's very important.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

  9. Back To Top    #9

    Re: Backwashing every three days - what's wrong?

    CYA is 20, which I learned from reading other posts, is low. 30 -50 is recommended. I'll get some and add it.

    Not sure what CH is. Calcium Hardness? It doesn't seem to be measured by our pool service.

    By the way, thanks for the good advice. I've learned a lot just today and will keep you posted on my progress.
    Mike Bowers
    Georgia, 44,000 gallon, in ground, salt water, gunnite

  10. Back To Top    #10

    In the Industry

    duraleigh's Avatar
    Join Date
    Apr 2007
    Location
    Sebring, Florida
    Posts
    30,083

    Re: Backwashing every three days - what's wrong?

    I would suggest 40-50ppm CYA in that pool.

    BTW, it is more than 39k if it has a deep end and your measurements are correct.

    CH is calcium hardness and, while it is a stable parameter, it is also quite important.

    read "The ABC's of Pool Water Chemistry" up in Pool School
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

  11. Back To Top    #11

    Re: Backwashing every three days - what's wrong?

    Chemical levels as of last night:

    FC: 4
    pH: 7.4
    TA: 100
    CYA: 60
    CH: 240

    The filter was backwashed July 3 in the a.m. pressues was 18 PSI. Next morning it was still 18 PSI. By Thursday a.m. it was 18 PSI. Late Thursday afternoon it had spiked to 28 PSI. The water is clear. Any thoughts on what causes the pressure to jump after a few days?
    Mike Bowers
    Georgia, 44,000 gallon, in ground, salt water, gunnite

  12. Back To Top    #12

    In the Industry

    duraleigh's Avatar
    Join Date
    Apr 2007
    Location
    Sebring, Florida
    Posts
    30,083

    Re: Backwashing every three days - what's wrong?

    Any thoughts on what causes the pressure to jump after a few days?
    What has your chlorine history been during that time? Has it stayed steady? How much have you added? How often?
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

  13. Back To Top    #13

    Re: Backwashing every three days - what's wrong?

    Shocked it on Monday and added CYA on Tuesday. Also added 80 pounds of salt. FC reading was 5+ for three days. Now 4. Before that we had trouble keeping the FC level up. It would fluctuate from 5 down to 1 over the course of a week.
    Mike Bowers
    Georgia, 44,000 gallon, in ground, salt water, gunnite

  14. Back To Top    #14

    In the Industry

    duraleigh's Avatar
    Join Date
    Apr 2007
    Location
    Sebring, Florida
    Posts
    30,083

    Re: Backwashing every three days - what's wrong?

    The times don't match up quite like they should but close enough to hazard a pretty accurate guess at what's happening....

    The filter is doing exactly as it is supposed to do...catching debris (in this case dead algae) and filtering it out of your pool water.

    Your fluctuating FC, your ability to hold FC with a SWG, all point to algae growing in your pool (even though you may or may not see it) and then being killed by a big dose of chlorine.

    If you haven't already done so, you need to backwash again.

    read "The ABC's of Pool Water Chemistry" up in Pool School

    If you can only test to 5ppm FC, you also need a much better test kit (FAS/DPD) to manage that big pool (and big investment)
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

  15. Back To Top    #15

    Re: Backwashing every three days - what's wrong?

    Quote Originally Posted by mbowers104
    Shocked it on Monday and added CYA on Tuesday. Also added 80 pounds of salt. FC reading was 5+ for three days. Now 4. Before that we had trouble keeping the FC level up. It would fluctuate from 5 down to 1 over the course of a week.
    By the way you are using the term "shocked" you are probably not actually shocking your pool. Shocking involves determining the correct shock level of FC (usually above 10ppm) and holding it there until

    1) the water is clear
    2) you lose less than 1ppm of FC overnight
    3) your CC is less than .5

    This pretty much always takes a few days. Adding a chemical called shock is not the same as shocking the pool.
    17,800 gallon, IG pool, 595 sq feet (17x35x4.5 avg rectangle), Hayward 525 cartridge filter, diamondbrite, 2 hp 2 speed hayward tristar filter, Stenner 45mhp10 automatically chlorinating

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •