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Thread: High FC clorine level, still have algae

  1. #1
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    High FC clorine level, still have algae

    This is my first posted question so I hope I'm posting in the right place. I have a 30,000 gallon L shaped vinyl liner pool. I've used the BBB method for three years with great results. This year is the exception. I have algae problems. Two days ago (Friday evening) I shocked with 9 lbs of sockit and put in 32 oz of algecide 60 on the advice of our pool store (first time I went there in three years). My readings on Friday from the pool store were FC 4.5, CC 6.1, PH 7.7, CH 77, TA 116 CYA 9. I'm using the trichlor tablets in the feeder so they said I didn't need to add any stabilizer.

    The next morning, I still had algae (slight) in the shallow end. Water is pretty clear, except when I sweep I can see the little green cloud of algae. I vacumed, backwashed, swept and added two more gallons of bleach. FC was at least 10 (my test kit stops at 10). I don't know what the CC was because my test kit doesn't show that. Swept again (morning and evening) and added 2 more gallons of bleach that evening.

    Next morning, still some algae. Swept again and added two more gallons of bleach (now I'm continuously vacumning). FC still reading above 10.

    I'm on my way to the store to find a test kit so I can test the CC but I'm extremely frustrated and broke! I have a sand filter, and we changed the sand last year and I cleaned the sand about a month ago.

    Any advice?

    Thanks! (just found this site and love it!)
    Helene Prince
    23,000 gallon in ground L Shaped Vinyl Pool, Barracuda vacumn, sand filter. Located in Virginia. Member since July 2010.

  2. #2
    Senior Member Richard320's Avatar
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    Re: High FC clorine level, still have algae

    Quote Originally Posted by Helene.Prince
    This is my first posted question so I hope I'm posting in the right place. I have a 30,000 gallon L shaped vinyl liner pool. I've used the BBB method for three years with great results. This year is the exception. I have algae problems. Two days ago (Friday evening) I shocked with 9 lbs of sockit and put in 32 oz of algecide 60 on the advice of our pool store (first time I went there in three years). My readings on Friday from the pool store were FC 4.5, CC 6.1, PH 7.7, CH 77, TA 116 CYA 9. I'm using the trichlor tablets in the feeder so they said I didn't need to add any stabilizer
    ....
    Helene Prince
    Is the CYA a typo? If it's really 9, it's too low. Sunlight is eating up the chlorine. If it's really 90, your shock level is 23 or above, and you may not be adding enough chlorine to really get ahead of the algae growth.

    To measure FC higher than your tester, dilute the sample. Mix 50/50 with distilled water, or if you have a water filter like a Brita, that should work, too. It just needs to be chlorine-free. Then take your reading and double it.

    You might also want to read this article/thread. There's also tons of information in Pool School; the link is on the upper right of every page.
    16K freeform gunite with spa; Pentair 4000 DE filter; Century Whisperflow 1 HP; Pentair Minimax heater.
    Troublefree does not mean Maintenancefree. It's like brushing your teeth: You can spend a couple minutes a day and pennies a week or go to the dentist once a year and spend several thousand dollars.
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    Re: High FC clorine level, still have algae

    Yes, the CYA level is just 9... It was zero 3 weeks ago and I added stabilzer in the sock method. Also I'm using the trichlor tablets to help get it up too. It was extremely high two years ago and I've had to work very hard to get it down over the last two years... might have taken it down too low though. Do you think I should add more stabilizer or continue with the trichlor tablets?

    I retested and my fc level is right at 10. I'm having some difficulty understanding the pool calculator... if my CYA is only 9, then what should my shock level be? I'm considering using the method I found here to increase my borates... not sure if that will help or not, but thought I might give it a try. In the years past, my pool has always stayed chrystal clear just using bleach and nothing else (PH & TC level's always stayed level).

    Thanks for your help.
    23,000 gallon in ground L Shaped Vinyl Pool, Barracuda vacumn, sand filter. Located in Virginia. Member since July 2010.

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    Re: High FC clorine level, still have algae

    Sorry... meant to say PH and TA level's always stayed the same...
    23,000 gallon in ground L Shaped Vinyl Pool, Barracuda vacumn, sand filter. Located in Virginia. Member since July 2010.

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    Administrator JasonLion's Avatar
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    Re: High FC clorine level, still have algae

    You need to get CYA up to at least 30 soon. Until you do that you will be losing too much chlorine to sunlight.

    Having your own top quality test kit would also save you a great deal of time, money, and trouble. Right now you appear to be guessing at amounts of chlorine to add, whic is sure to be either too little or too much, causing problems either way.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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    Re: High FC clorine level, still have algae

    Thanks for your reply. I plan to order the TF100 soon. I just bought some Aquachek test strips from Lowes and it says my CYA is 30 now. Since I've been blasting the trichlor tablets in the chlorinator for three days to get the CYA up I'm not sure if this is acurate or not, but until I get the TF100, I'll assume it is to avoid the CYA getting to high again.

    The test shows my TC at 10 and the FC at 10. The water is completely clear now, but I still see a small amount of algae on the steps. I swept everything again and ran the backwash until the water was completely clear. Based on the CYA chart, I need to get the FC up to 12 so I'll add 1 1/2 gallons now and check the levels again at the end of the day (it's cloudy today so instead of waiting until tonight I'll go ahead now).

    So I hope I'm understanding everything correctly... I really like this website!
    23,000 gallon in ground L Shaped Vinyl Pool, Barracuda vacumn, sand filter. Located in Virginia. Member since July 2010.

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    Re: High FC clorine level, still have algae

    Quote Originally Posted by Helene.Prince
    Yes, the CYA level is just 9... It was zero 3 weeks ago and I added stabilzer in the sock method. Also I'm using the trichlor tablets to help get it up too.
    Let's start there. How much stabilizer did you add? I assume you used the Pool Calculator, what was the goal for that volume added?

    Ho many trichlor tabs have you used since the CYA 0 reading? Just a guess per week or a total number if you know, and we need to know the volume of each tablet since they do vary.

    We ought to be able to calculate what the additions total so far. While there is some decay of CYA it isn't all that much over a span of weeks. As you know, right now the CYA is not showing up on test though it should later on. We can base the chlorine additions on the calculated CYA for now.
    23,000 gallon in ground pool with rock waterfall and spillover spa, Aqualink control system, Polaris 380 cleaner, Purex Triton Clean&Clear Plus cartridge filter. Located in The Woodlands, Texas.

    Pool owner since Nov 2008, Trouble Free since April 2009. Happy to help when I can.

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    Re: High FC clorine level, still have algae

    I added five lbs of stabilzer three weeks ago. I started using the trichlor tablets for the last three weeks (3 inch size). I guess I've put in two at a time every other day for the last three weeks or so with the flow set to full. I didn't use the pool calculator when I did this because I hadn't found this website until now.

    We have had very little rain here, so I have had to add quite a bit of water too. I'd guess in the last three weeks I've had to add about 5 inches of water and the pool hold 30,000 gallons. The test strips show the CYA at 30... and the FC at 12 right now. Swept about 3 hours ago and saw slight algae... just swept it again and saw more slight algae so I added another pound of sockit (that was my last bag so I'll be using bleach from now on.)
    23,000 gallon in ground L Shaped Vinyl Pool, Barracuda vacumn, sand filter. Located in Virginia. Member since July 2010.

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    Re: High FC clorine level, still have algae

    Ok, now, Helene, you need to start keeping these records. That way you can use the Pool Calculator and you will know what is happening.

    Pool size 30,000. Down at the bottom of Pool Calculator, Effects of adding Chemicals; 5 lbs = 80 oz stabilizer... will raise CYA by 20 ppm.

    Tablets, two every other day for 3 weeks = 21 tablets. You still need to look at the box and see the weight, I will assume 7 oz each since mine are that but they do vary from brand to brand. So, 21 x 7 = 147 oz trichlor...will raise CYA by 20. Test strips show 30 and we calculate 40.

    Stop the tablets now. CYA of 40 is enough until you get the algae all under control. Take the FC up to 15 shock level for CYA of 40.

    Now, I do not know what SockIt is. Search online reveals that is 53% cal-hypo. That is fine your CH was only 77 earlier, I assume this is vinyl or else this is too low and could be an issue to look at later.

    For now, use the testing you have and dilute the pool water by an equal amount of distilled water, then test. Multiply the result by 2. This will let you read up to 20 ppm instead of just 10 ppm though you lose some accuracy.

    Keep brushing and keep FC up to 15 at all times, it is OK to go a bit over but try to not go much under. Run the filter 24/7 and clean as needed.
    23,000 gallon in ground pool with rock waterfall and spillover spa, Aqualink control system, Polaris 380 cleaner, Purex Triton Clean&Clear Plus cartridge filter. Located in The Woodlands, Texas.

    Pool owner since Nov 2008, Trouble Free since April 2009. Happy to help when I can.

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    Re: High FC clorine level, still have algae

    That's a good idea about writing everything down. I've never kept up with everything in the past but I I think that is a great idea.

    I started using the Sockit because the pool calculator said it would increase the CH. The package says that 1 lb is 62% cal hypo. Over the weekend I've added a total of 13 lbs of sockit, so the CH should be higher than it was Friday. I'm putting the tablets away for now and will test the FC and CH level in about an hour and then use the pool calculator to determine how much bleach to add to get it up to 15.

    Thanks for all your help!
    23,000 gallon in ground L Shaped Vinyl Pool, Barracuda vacumn, sand filter. Located in Virginia. Member since July 2010.

  11. #11
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    Re: High FC clorine level, still have algae

    Again, I don't see what your pool type is, so CH may or may not be important. If it is plaster, I suggest you bite the bullet and get some calcium increaser, 77 CH is way low for plaster. If it is vinyl, it doesn't matter -- you just want the cheapest source of chlorine whether that is bleach or cal-hypo. I can tell you that the 1 lb bags of cal-hypo are likely not economical but in the 100lb bucket it may be.

    You can add the details of your pool in your signature, go to the User Control Panel, top left, find Profile (?) then signature (?). I'd try to flip back to see if you gave that info but... it is my 30th wedding anniversary and we are off to dinner in moments.
    23,000 gallon in ground pool with rock waterfall and spillover spa, Aqualink control system, Polaris 380 cleaner, Purex Triton Clean&Clear Plus cartridge filter. Located in The Woodlands, Texas.

    Pool owner since Nov 2008, Trouble Free since April 2009. Happy to help when I can.

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    Re: High FC clorine level, still have algae

    I updated my signature, let me know if I need to add anything else.

    My pool has a vinyl liner. I bought the cal-hypo at a good sale price when I started having algae problems because I started doubting my bleach method and thought I would give it a try to see if it would work better. Now I realize that I wasn't getting my chlorine level up high enough.

    This morning the FC was still at 15 and I didn't see any algae when I swept with the pool light on, but it was still dark when I left for work so I'm not 100% sure. I added another gallon of bleach to be on the safe side. When I get home this evening I'll check everything to make sure the algae is gone for good (I hope!)

    Thanks for your help and I hope you had a wonderful anniversary dinner. My husband and I will celebrate our 27th anniversary this year...
    23,000 gallon in ground L Shaped Vinyl Pool, Barracuda vacumn, sand filter. Located in Virginia. Member since July 2010.

  13. #13
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    Re: High FC clorine level, still have algae

    Cal-hypo is good to have on hand and you can use it whenever you wish as your CH is very low and CH won't be a problem for awhile yet. When you use the Pool Calculator, just notice the SCI value at the bottom, if it starts to get toward the outer limits then you will need to do something, but that may never happen.

    Still, bleach is better in that it adds nothing but chlorine to the pool, that is no CH and no CYA. And is typically cheaper.

    Otherwise, I think you are in good shape. Keep FC up to 15, filter and brush. Do look in all the nooks and crannies for hidden algae if you have any spots like that. All that needs to be brushed to expose the algae to chlorine, live algae hides under the shell of dead algae so brushing is important.

    Next time, come here first instead of the pool store; the $ spent on the test strips, algaecide, and bags of cal-hypo would have been better spent on bleach and the TF-100.
    23,000 gallon in ground pool with rock waterfall and spillover spa, Aqualink control system, Polaris 380 cleaner, Purex Triton Clean&Clear Plus cartridge filter. Located in The Woodlands, Texas.

    Pool owner since Nov 2008, Trouble Free since April 2009. Happy to help when I can.

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    Re: High FC clorine level, still have algae

    Ok, I realized that I made a huge mistake in calculating the size of my pool. Years ago, the pool store said my pool held 32,000 gallons. I measured everything myself and calculated the pool size as 23,000 gallons instead. Huge difference! That explaiins why when I put in the required amount of bleach it went up to 20 ppm instead of 15 ppm!

    I drained off about a 1/4 of the water and replaced with water from the well (to get the CYA down some) and have kept the FC at 15 for the last two days and swept off and on all day yesterday. I didn't see any algae this morning when I swept, but it was still dark and the FC was still at 15 as well. My CYA appears to be between 30 and 40 now. So I think everything is all straight (will know for sure when I get home today and sweep for algae.) In the dark this morning with the light on in the pool, the water was chrystal clear and sparkling!

    Thanks for everyone's help! I have one question. The PH was at 7.9 and the TA was around 200 this morning. Is that because the chlorine level is so high and will it come down on it's own as the chlorine comes down? I plan to keep and eye on that but I was curious if I need to stop by the store on the way home and get some muritic acid just in case. I have about 2 lbs of PH down at home I could use instead of the muritic acid.
    23,000 gallon in ground L Shaped Vinyl Pool, Barracuda vacumn, sand filter. Located in Virginia. Member since July 2010.

  15. #15
    Administrator JasonLion's Avatar
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    Re: High FC clorine level, still have algae

    High FC levels will tend to cause PH to read higher than actual. One the other hand, with TA around 200, the PH will tend to go up on it's own. Wait till the FC level comes back down to normal before worrying about the PH.

    How did TA get up to 200, when it was 116 earlier? TA doesn't tend to go up on it's own. Perhaps your TA reading is incorrect?
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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    Re: High FC clorine level, still have algae

    I've noticed that my TA and PH have been higher this year than normal and I think it's related to my well water. Normally I don't add that much water during the year because of rain. But we are having a severe drought this year and I've had to add a lot of water this year.
    23,000 gallon in ground L Shaped Vinyl Pool, Barracuda vacumn, sand filter. Located in Virginia. Member since July 2010.

  17. #17
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    Re: High FC clorine level, still have algae

    Ah, that makes sense. You should test the TA level of your fill water to double check that is what is happening.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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  18. #18
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    Re: High FC clorine level, still have algae

    Do not trust the strips for a CYA level. They are simply not accurate.
    Helpful links: Pool School; CYA/Chlorine Chart
    24' round AG pool, 52" high, Raypak heater; Waterway 2 spd Pump;
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  19. #19
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    Re: High FC clorine level, still have algae

    I really don't trust the test strips either, but that's all I have for now. I can't afford to get the TF100 right now (sick horse, son just got married, way too many expenses). I plan to get the TF100 for next year. I'll get the pool place to check it for me soon, but they are about 40 miles away in the opposite direction from where I work. So in the mean time, I'll go by the test strips and keep my eyes open for algae and adjust accordingly.
    23,000 gallon in ground L Shaped Vinyl Pool, Barracuda vacumn, sand filter. Located in Virginia. Member since July 2010.

  20. #20
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    Re: High FC clorine level, still have algae

    I'm sorry for the troubles - completely understand...

    Just keep in mind - we have thousands of reports of test strips putting CYA levels all over the place, and never accurately.

    back when I used strips they read 30-50 and my level was actually well over 100. Pool store testing unfortunately can be inaccurate too, so just be wary.

    Walmart sells a cheap $20 6 way drop based kit by HTH that includes a CYA test - it has enough reagent for 2 tests.
    Helpful links: Pool School; CYA/Chlorine Chart
    24' round AG pool, 52" high, Raypak heater; Waterway 2 spd Pump;
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