Become a TFP Supporter Pool Math Forum Rules Pool School
Results 1 to 2 of 2

Thread: FC Test flashes red then clear after adding R-870 etc...etc

  1. Back To Top    #1

    FC Test flashes red then clear after adding R-870 etc...etc

    When I opened my pool this year, I did the ritual thing to take a water sample to my usual pool dealer to have it analyzed. Up to this time I was using test strips to spot check the water balance. The guy at the store told me my cya was over 100 but the other readings (pH, FC, TA,CH) were within the normal range. Since he used a machine to perform the test, I asked for a printout. No can do, he said. His printer was broken. Then I thought about getting some info on pool test kits. In the past I used them but either I didn't do the tests right or the kit directions left a lot to be desired, thus relying on the test strips. Surfing the Web, I came across this site and I was intregued with the wealth of information on kits and testing. In the past I relied on the test strips to guide me on how much Chlorine or baking soda to add, but that was just getting me in the neighborhood as to where the readings should be. For the past 5 years I just added stabelizer and 3" Chlorine pucks, not knowing this was adding to my total CYA. I also found the Pool Calculator on http://www.poolcalculator.com/ which your site recommended. I downloaded the calculator simply by right clicking on the When I opened my pool this year, I did the ritual thing to take a water sample to my usual pool dealer to have it analyzed. Up to this time I was using test strips to spot check the water balance. The guy at the store told me my CYA was over 100 but the other readings (pH, FC, TA,CH) were within the normal range. Since he used a machine to perform the test, I asked for a printout. No can do, he said. His printer was broken. Then I thought about getting some info on pool test kits. In the past I used these kits but either I didn't do the tests right or the kit directions left a lot to be desired, thus relying on the test strips. Surfing the Web, I came across this site and I was intrigued with the wealth of information on kits and testing. In the past I relied on the test strips to guide me on how much Chlorine or baking soda to add, but that was just getting me in the neighborhood as to where the readings should be. For the past 5 years I just added stabilizer and 3" Chlorine pucks, not knowing this was adding to my total CYA. I also found the Pool Calculator on http://www.poolcalculator.com/ which your site recommended. I downloaded the calculator simply by right clicking on the calculator page and saving it as an .htm file on my C:\drive. I then went to the file on C:\ drive and generated a desktop icon. Any time I need it, I just click on the icon and Viola!. I decided to buy the TF-100 Kit this past June. When I got the kit, the first thing I did was design a pool log sheet where I would log the Date,TC,FC,CC,TA,pH,CH,CYA and Notes. Now feeling organized, I looked the kit over and thought how simple the instructions were. On the first go round, I saw my CYA was completely out of range. I had to dilute the sample with an equal amount of fresh water and re-run the test. The result was a CYA reading of 190. This is a result of using those Chlorine pucks and bags of pool "shock" over the past 5 years. The only way to get the CYA down was to drain some of the pool water. I have a 15' by 5' round pool with about 5000 gallons of water. Using the Pool Calculator, it told me to drain 80% of the water to get the CYA down to 40. That's 4000 gallons of water. Well I did that and after refilling the pool back up, I took another reading and the CYA read 80. Maybe I didn't drain enough water. Now the Calculator said to drain another 50%. That's 2500 gallons. Apparently not draining the recommended amount the first time caused me to have to drain 50% of a lower CYA reading water. Out went another 50%. After refilling the pool again, my CYA was finally at about 40. I decided to take a water sample to the pool store to see what they came up with on the CYA reading. Their reading was 30%. Good enough. I then decided NEVER to add any store bought chemicals to the pool anymore. I will use the BBB method recommended on this site which is located in the Pool School section. Now with baking soda, 6% bleach, and Boric Acid on hand, I started testing the pool water. After going slowly through the tests for a couple days, I felt a lot better about running these tests. By the end of June, I ran so many tests I started getting low on chemicals so I cut the tests back to twice a week. The pool isn't used that much so human pollution was a non-issue. Today, after letting the tests lapse for two weeks and after a week of heavy rain, I ran the tests again. My first test was to check FC. I filled the test tube to the 10mL mark and added one heaping spoon of R-870. As soon as the R-870 mixed with the water sample, it turned red and suddenly turned clear again. Now that's unusual. Normally the mixture would turn red and stay red if there was Chlorine in the sample, or not change if Chlorine was absent. I wondered if the R-870 lost it's kick. I looked around on the internet and found a site where it was explained that when R-870 loses it's strength, it turns an ash or gray color. My R-870 looked more whitish gray than gray. It also explained that when the R-870 was aging, more than one spoonful could be added without distorting the test readings. Well, I decided to get a sample of fresh water and add a small smidgen of 6% bleach and test that. Lo and behold, the sample turned red and stayed red after adding R-870, so I knew that was not the problem. What I did eliminate was the combined chlorine. Maybe the CC was completely out of range. So to reduce the CC, I added 150 oz. of 6% bleach and let to filter run for a couple hours. I then took another sample and ran the FC test again, and sure enough, the sample went from red to clear again as soon as I added the R-870. Now I know the R-870 is not the problem. So what's the problem? More internet searching. I came across a school site that explained how to run tests on pool water. SNIP:"If you get no color at all you may have too much chlorine present and it is bleaching out the reagent color. This is the problem when you see a bright red flash as you put the R-870 just before it turns clear, or if you can smell chlorine on your wet hand, yet the test result is colorless. Depending on the pH, a chlorine tests that bleaches out often indicates chlorine levels above 20ppm and requires a dilution with distilled water (or tap water) to get a reading." I did that and sure enough, my FC was 29. I also checked my pH and the sample turned purple, another sign of over chlorination. For my 5000 gallon pool, I added 24 oz. of Leslie's Chlor Neutralizer. After an hour running the Diatomaceous earth type pump, I re-ran the FC test normally and I got a reading of 6. Still a little high, but good enough for now. My pH went back down to 7.4. The rest of the tests were CC:0, TA:90, CH:150, CYA about 30. How's that for a learning curve? My wife calls me the mad chemist. But that's all right for being 72 years old. Never too old to learn. To sum up this story, when pH test turns purple or FC test flashes red and back to clear, that indicates that there is too much Chlorine in pool. End of story. Oh, as a final Note: I set my Boron level to 50 to stabilize upper range of my pH using Roach Away. And it makes the pool water sparkle. Walmart sells "Roach Away" in 1 pound bottles for $2.98. MSDS shows it contains 99.9% Boric Acid. Just don't tell anyone. I used 15 bottles to get Boron reading of 50 for a 5000 gallon pool. I didn't want to go the Muriatic acid and Borax route. This was simple. Pour the roach powder in and you're all set. pH barely moved at all.

  2. Back To Top    #2

    Join Date
    Mar 2007
    Location
    San Rafael, CA USA
    Posts
    12,082

    Re: FC Test flashes red then clear after adding R-870 etc...

    Welcome to TFP!

    Thanks for sharing your story. If you get the flash of color or that it doesn't hold for the chlorine test, you can also just add more DPD powder and if the color holds, then do the test as normal, though since you know the FC will be high you may want to start over with a 5 ml sample where each drop is 1 ppm FC (to save on reagent). Nice tip about the Roach Away for about $3 per pound. In bulk at The Chemistry Store, 15 pounds of boric acid is $1.85 per pound (plus shipping) or $2.52 per pound for 15 pounds (or seemingly $2 per pound for 15 1-pound) at DudaDiesel or $2.25 per pound for 4 pounds from AAA Chemicals, but again one must add shipping costs.
    16,000 gallon outdoor in-ground 16'x32' plaster pool; Pentair Intelliflo VF pump; Pentair IntelliTouch i9+3s control system; Jandy CL-340 square foot cartridge filter
    12 Fafco solar panels; Purex Triton PowerMax 250 natural gas heater (200,000 BTU/hr output); automatic electric pool safety cover; 4-wheel pressure-side "The Pool Cleaner"

Posting Permissions

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