Become a TFP Supporter Pool Math Forum Rules Pool School
Results 1 to 10 of 10

Thread: Increasing FC Test Result

  1. Back To Top    #1

    Join Date
    Dec 2012
    Location
    Frisco, TX
    Posts
    40

    Increasing FC Test Result

    I have had two instances where my FC has risen between two FAS-DPD tests with no bleach or other chlorine being added to the pool. The tests have usually been spaced apart by 8 - 12 hours. It happened last night and I am trying to figure out why. I know it has to be operator error of some sort. Last night I tested at 10:30pm and got a reading of FC 4.5 / CC 1.0. I tested again this morning and got FC 6.0 / CC 0.5. Both tests where it increased were OTCL tests and both evening tests showed CC of 1.0. It also has been early in the week after a weekend of swimming. The other time it happened my first test was FC 14.0 / CC 1.0 and the second was FC 16.0 / CC 0.5.

    I test with a Speedstir and use the TF100 kit. My kit is less than two months old and stored inside.

    I don't understand how there can be an increase overnight so I know I must be doing something wrong. I know one possibility is that in performing the FC test, maybe I did not get my FC test water totally clear and I needed to add one more drop of R-871. As the water clears, I am usually very conservative about adding that extra drop. If I am "on the fence" as to whether think its totally clear or not I don't add it. I would rather have a slightly low reading of FC than a high reading. That would would possibly account for 0.5 of the difference between evening and morning.

    The other possibility I am contemplating is the R-870 powder. The instructions call for one heaping scoop. Everyone interprets heaping differently and I can honestly saying that I have difficulty in making my "heaping" exactly the same from one test to the other. I am wondering if slight differences in the R-870 powder could be driving this as well. Is the test very sensitive to the amount of R-870 powder? Post #2 in this thread seems to indicate that not enough R-870 powder could impact the test.

    http://www.troublefreepool.com/help-...00-t38295.html

    Thoughts?
    22K Gal, Chlorine, IG, Pebble Sheen Plaster, Jandy 60Sq Ft DE Filter, Intelliflo 3HP VS pump with SVRS, Rainbow 320 Chlorine Dispenser
    Other Equip - Jandy PDA PS6, Jandy LRZ400 Heater, Polaris 280 vacuum
    Features - Spa with fountain that empties into pool over waterfall spillway and separate table rock waterfall, Pool gets full sun until later afternoon and then partial sun
    Pool completed and filled 6/28/13

  2. Back To Top    #2
    Mod Squad Bama Rambler's Avatar
    Join Date
    Jun 2009
    Location
    SouthWest Alabama
    Posts
    22,345

    Re: Increasing FC Test Result

    Do you have any tablets in that tablet feeder?
    How long after the last addition of chlorine did you do the evening test?
    Dave J. TFP Moderator
    24' x 52" Round AGP. 2hp/¼hp SPL Power-Flo 2-speed pump. 200sqft Waterway Cartridge Filter. 45MHP2(3GPD) Stenner Peristaltic Pump
    Pool School ----- Pool Math ----- TF-Test Kit

  3. Back To Top    #3

    In the Industry

    duraleigh's Avatar
    Join Date
    Apr 2007
    Location
    Sebring, Florida
    Posts
    30,082

    Re: Increasing FC Test Result

    The correct amount of powder is really not very critical. If the solution turns pink/red, you have chlorine in your pool and the powder is adequate for the test. Some rare, rare exceptions but not at your FC levels.

    The first thing that comes to my mind is the importance of carrying the test to completion. Your last drop of R-0871 should produce ABSOLUTELY no further color change to the solution. You than subtract that drop that had no effect and the result is your FC.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

  4. Back To Top    #4
    linen's Avatar
    Join Date
    Jul 2010
    Location
    Twin Cities, MN
    Posts
    8,649

    Re: Increasing FC Test Result

    As duraleigh said, make sure you carry the test out to completion. Make it a habit of adding the extra drop even thought the solution may appear clear to be certain there is no more change and make sure you have good lighting when doing the test. One reason for this is if you skimp on the R-0870, the end point is still there but can be hard to discern.
    TFP Expert who uses Pool School and my TF100 test kit along with PoolMath for my: Round 11K gallon AGP with deep end, 20" sand filter, Matrix 1hp 2spd, 6 2ftX20ft solar panels (and solar cover!), Intex SWCG (copper bars disconnected) and a Rubadub hot tub (chlorine). The SLAM process is not finished until: 1. CC < 0.5 ppm, 2. An OCLT < 1.0 ppm and, 3. The water is crystal clear.

  5. Back To Top    #5
    Mod Squad jblizzle's Avatar
    Join Date
    May 2010
    Location
    Tucson, AZ
    Posts
    37,389

    Re: Increasing FC Test Result

    Are you using the light on the Speedstir? I found that it was harder to see if the water was truly clear with that LED on ... so I never turn it on.
    Jason, TFP Moderator
    18k IG pebblesheen pool, Hayward ProLogic P4 w/ T-15 SWG, Pentair 1HP 2-speed Superflo, Hayward 6020 DE filter
    500 sqft Heliocol solar panels, ThePoolCleaner, TF-100 test kit w/ SpeedStir
    Pool School + Test Kit + PoolMath = A TROUBLE FREE POOL
    If you found TFP helpful and we saved you money ... Become a TFP Supporter!

  6. Back To Top    #6

    Join Date
    Dec 2012
    Location
    Frisco, TX
    Posts
    40

    Re: Increasing FC Test Result

    No pucks. Used them when we filled to pool at the end of June to build up CYA but stopped several weeks ago when I got to a CYA of 40.

    In both cases, no bleach had been added at least 20-24 hours before either of the evening tests.

    Thanks for the advice on the last drop

    Not using the light on the Speedstir. I agree on its effect in evaluating the water
    22K Gal, Chlorine, IG, Pebble Sheen Plaster, Jandy 60Sq Ft DE Filter, Intelliflo 3HP VS pump with SVRS, Rainbow 320 Chlorine Dispenser
    Other Equip - Jandy PDA PS6, Jandy LRZ400 Heater, Polaris 280 vacuum
    Features - Spa with fountain that empties into pool over waterfall spillway and separate table rock waterfall, Pool gets full sun until later afternoon and then partial sun
    Pool completed and filled 6/28/13

  7. Back To Top    #7

    Join Date
    May 2013
    Location
    Bay City, Michigan
    Posts
    283

    Re: Increasing FC Test Result

    Your not adding the stir bar until you have the proper amount of water measured every time correct?
    12500 gallons, 24 foot round above ground
    Hayward Sand filter, Pentair OptiFlo 1HP 2-Speed pump

  8. Back To Top    #8

    Join Date
    Dec 2012
    Location
    Frisco, TX
    Posts
    40

    Re: Increasing FC Test Result

    That is correct. Put the water in and then add the stir bar. I am baffled by this honestly. I will try adding the extra drop as suggested but even then it doesn't make sense that I would have such a large variance.
    22K Gal, Chlorine, IG, Pebble Sheen Plaster, Jandy 60Sq Ft DE Filter, Intelliflo 3HP VS pump with SVRS, Rainbow 320 Chlorine Dispenser
    Other Equip - Jandy PDA PS6, Jandy LRZ400 Heater, Polaris 280 vacuum
    Features - Spa with fountain that empties into pool over waterfall spillway and separate table rock waterfall, Pool gets full sun until later afternoon and then partial sun
    Pool completed and filled 6/28/13

  9. Back To Top    #9

    Join Date
    Jul 2013
    Location
    Columbus, Ohio
    Posts
    114

    Re: Increasing FC Test Result

    Quote Originally Posted by Bevostein
    That is correct. Put the water in and then add the stir bar. I am baffled by this honestly. I will try adding the extra drop as suggested but even then it doesn't make sense that I would have such a large variance.
    How are you holding the bottle? I read in another thread that holding the bottle perpendicular to the test vial instead of vertical affects the size of the drops. That would throw your tests off if you don't hold the bottle of reagent the same way each time.
    16,500 gallon, 18" x 38" Grecian; IG Vinyl, Hayward DE

  10. Back To Top    #10

    Join Date
    Dec 2012
    Location
    Frisco, TX
    Posts
    40

    Re: Increasing FC Test Result

    I saw that post as well while doing some searches to try and figure it out. I do hold it straight vertical. I do apply a slight amount of pressure to get the drops to drip out. I have seen comments that the correct procedure is to squeeze to get the reagent on the tip of the bottle and then let gravity pull it out. I think I have been consistent in how I do it but maybe the squeeze pressure has been different between the evening and morning.
    22K Gal, Chlorine, IG, Pebble Sheen Plaster, Jandy 60Sq Ft DE Filter, Intelliflo 3HP VS pump with SVRS, Rainbow 320 Chlorine Dispenser
    Other Equip - Jandy PDA PS6, Jandy LRZ400 Heater, Polaris 280 vacuum
    Features - Spa with fountain that empties into pool over waterfall spillway and separate table rock waterfall, Pool gets full sun until later afternoon and then partial sun
    Pool completed and filled 6/28/13

Posting Permissions

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