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

Thread: Treating a partially drained pool full of algae

  1. Back To Top    #1

    Treating a partially drained pool full of algae

    My cya is at 100 and the pool is as thick with green as pea soup. I am in the process of draining 60 percent of the water to reduce the cya to 40. Soon I will have a 9600 gallon pool of pea soup instead of the original 24,000 gallon. At that point, I cannot use the filter. Should I shock the 9600 gallons to 25ppm (as per the pool calculator) or should I fill the pool, retest and balance the chemicals and shock from there?? All help most appreciated and much needed.
    San Diego, CA
    24,000 gal. 15x40 IG plaster
    Hayward Star Clear Plus 120sq.ft. cartridge filter
    1.5 HP
    In line chlorinator using triclor

  2. Back To Top    #2
    Casey's Avatar
    Join Date
    Apr 2007
    Location
    SW PA
    Posts
    10,157

    Re: Treating a partially drained pool full of algae

    I'd fill it back up and then shock it.

    That's what I'd do.

    Welcome to TFP!
    I'd bet you my bikini you'll never get TFP water from a pool store!

    24' Sharkline Venture De Filter

  3. Back To Top    #3

    Join Date
    Dec 2007
    Location
    Central New York
    Posts
    504

    Re: Treating a partially drained pool full of algae

    What type of pool?
    How did it get green?


    If it is an IG, I wouldn't drain 60% of the water out of it. Do you know how the water table is in your area? I would drain down to about one foot below the skimmers and refill. Take some reading before I would drain again to a foot below the skimmers and refilling. Of course a lot depends on what type of pool you have.

    What are the other reading of your pool water?
    Hotrod30

    20 X 40 foot vinyl Borates and Salt Pool
    Rolachem Chlorine Feeder
    Hayward 27 inch sand filter with 80 lbs of pea gravel
    Jacuzzi Splash Pak SP55 DE filter in parallel
    Pentair VF3050 pump

  4. Back To Top    #4
    TizMe's Avatar
    Join Date
    Aug 2007
    Location
    Covington, Georgia
    Posts
    920

    Re: Treating a partially drained pool full of algae

    Welcome to TFP !

    First a trip to the store to get SEVERAL jugs of chlorine is in order. When you think you have enough in the cart put more in
    You will also need a reliable test kit so you can test your own water.

    Refill your pool and test your water to see what your CYA is then bring it to shock levels according to the CL/CYA shock chart listed in my signature.
    You will need to run your filter 24/7 until the water is clear.
    Lots and lots of brushing is needed as well as back washing your filter.

    Read our Pool School area of the forum. There is a lot of wonderful info to help you get your water crystal clear! Also in my signature is a link to a pool calculator which will help you to figure how much of your chemicals to add to your pool.

    If your able to post some pictures so we can follow the transformation of your pea soup to a clear oasis.
    It would also help if you put your pool type vinyl, gunite, fiberglass. AG, IG and equipment you have in your signature too.

    Clearing your pool is going to take several days so you will need some POP (Pool Owners Patience)

    Good Luck !! If you have more questions post back and someone will help you
    Les
    Don't have a pool right now. Just sharing what I have learned over the years!
    Helpful Links:
    Pool School,Pool Calculator,Cl/CYA Shock Chart,TF Test Kit
    Doing BBB and loving it!

  5. Back To Top    #5

    Re: Treating a partially drained pool full of algae

    I live in San Diego and the pool is on top of a hill. I do not know where the water table is, but it is no where near the pool and is not a factor in the draining. The pool has not been drained in the 12 years that I have lived here, nor had it been drained by the previous owner who lived here for 8. The evaporation rate is high and the water is necessarily replenished daily nearly year round.

    The PH is 7.6 and TA is 60. The sanitizer is triclor. The FC is 5.0 and the amount of chlorine need to shock is ridiculous.

    Actually, I believe I can run the filter to pull only from bottom. The only reason I was thinking of shocking prior to filling was to concentrate the chemical more and kill off as much as I can before filling the pool. Is this a bad idea?
    San Diego, CA
    24,000 gal. 15x40 IG plaster
    Hayward Star Clear Plus 120sq.ft. cartridge filter
    1.5 HP
    In line chlorinator using triclor

  6. Back To Top    #6
    TizMe's Avatar
    Join Date
    Aug 2007
    Location
    Covington, Georgia
    Posts
    920

    Re: Treating a partially drained pool full of algae

    Thats what shocking your pool does however you need to have it filled so as the algae dies off it is filtered out of the water. How many gallons does your pool hold, what type of filter do you have? It would help us if you could put this information in your signature.
    Les
    Don't have a pool right now. Just sharing what I have learned over the years!
    Helpful Links:
    Pool School,Pool Calculator,Cl/CYA Shock Chart,TF Test Kit
    Doing BBB and loving it!

  7. Back To Top    #7

    In the Industry

    duraleigh's Avatar
    Join Date
    Apr 2007
    Location
    Sebring, Florida
    Posts
    30,084

    Re: Treating a partially drained pool full of algae

    rbkl,

    I understand your reasoning.

    However, an important part of the clearing process is removing a lot of the gunk thru filtration which means filling the pool back up. Overall, I think you'll find it easier to deal with a full pool so you can use your circulatroy system to help clean up.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

  8. Back To Top    #8

    Re: Treating a partially drained pool full of algae

    Okay. I did drain the pool 60%. After reading your advice, I decided that I would refill the pool prior to treatment. It was late last night when I went outside and saw that pool with just that bit of water and thought again how little liquid chlorine it would take to get to a shock rate, (and maybe get a jump on the green) and so...., I added chlorine to 25ppm and thought I would start filling the pool first thing in the morning.

    This morning, the green was ever so slightly lighter, but you still could not see the bottom in less that 2 feet of water. Before I turned the fill water on, I took a sample down to the pool store just to see what the FC was. They said it was "well over" 30ppm. These are the same folks who said my CYA was 100. They now say the 100 was the ceiling of what they could measure and that the CYA may be very considerably higher. They believe this to be so because the algae was so little affected by so high a FC rate. They recommend that I drain a half of what is left in the pool. They are so confident of this that they promised they would give me liquid CYA to bring my filled pool up to 30 CYA for free should it be below that level. Should I take him up on this? I live in very sunny southern CA and would not want too low of a CYA level. I read on line that desert areas keep their CYA near 90. My goal was 40 - 60. Is my goal a good one?
    San Diego, CA
    24,000 gal. 15x40 IG plaster
    Hayward Star Clear Plus 120sq.ft. cartridge filter
    1.5 HP
    In line chlorinator using triclor

  9. Back To Top    #9
    JasonLion's Avatar
    Join Date
    May 2007
    Location
    Silver Spring, MD
    Posts
    37,879

    Re: Treating a partially drained pool full of algae

    It is very difficult to get any kind of accurate CYA reading when the water is cloudy/murky. Most of the tests will read higher than actual when the water is cloudy/murky. So there really is no telling what your CYA level is.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
    Creator of PoolMath and Pool Calculator. Other handy links: Support this site, TF Test Kits, Pool School

  10. Back To Top    #10

    Re: Treating a partially drained pool full of algae

    Can you use the Pool Calculator in reverse, that is, if you know all your pool values except CYA and a known shock level has no effect, can you say where the CYA is generally?
    San Diego, CA
    24,000 gal. 15x40 IG plaster
    Hayward Star Clear Plus 120sq.ft. cartridge filter
    1.5 HP
    In line chlorinator using triclor

  11. Back To Top    #11

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

    Re: Treating a partially drained pool full of algae

    It unfortunately doesn't work that way since the recommended shock level is for a rough rate of killing the algae -- not a precise thing. However, I'll take a stab at this since you did see things get slightly lighter green at 25 ppm FC so let's say this is perhaps double the rate of just keeping up with algae growth and let's say that's around an FC of 5% of the CYA level. So if 25 ppm FC were about 10% of the CYA level, that would be a CYA of 250 ppm. This is, of course, a total guess -- it could be 150 ppm or it could be 300 ppm. Even if it were 100 ppm CYA, then a half drain would not be bad and given their offer of free liquid CYA (probably "Instant Pool Water Conditioner") you don't have much to lose.

    As Jason wrote, you unfortunately can't rely on the CYA test very much when the water is murky with algae. Nevertheless, if you can take the pool water by itself (i.e. don't add any reagent to it) and clearly see the black dot filling up all the way to the top of the tube, then that's only going to affect the CYA test if it had actual low values (so would read higher). If it reads 100 ppm then the murkiness won't affect that very much unless it was REALLY murky (and since you can see a couple of feet, that may not be enough to affect already high readings on the CYA test).

    If you want, you can do a test in a bucket of pool water to see the effects of chlorine and how much it takes to kill the algae (you can do this while doing the half drain/refill). If you have a 2 gallon bucket (preferably white or light-colored), then every teaspoon of 6% bleach adds 40 ppm FC. Look at this thread and notice that after 10 minutes of shocking the pool gets noticeably better with clearing of much of what is in the water leaving more solids on the bottom to deal with (of course, this situation is on pool opening). So you can see how much chlorine it takes to find a noticeable difference in the bucket which you should keep outside exposed to sunlight so that the algae grows just as it may still be doing in the pool.

    Also, you should really, really get your own good test kit such as the TF100 from tftestkits.com here. Though this pool store you are using sounds more decent than most (they seem to have some understanding of the chlorine/CYA relationship), you're going to need your own good test kit in the future so should just get that now. In the meantime, keep the FC level up in the pool using chlorinating liquid or 6% unscented bleach if you can, just so you keep the algae somewhat at bay. If you wanted to use Cal-Hypo for shocking, you could do that if your Calcium Hardness (CH) isn't too high -- I suspect it's low due to the drain/refill depending on the CH of your fill water.

    Though you said your pool was 24,000 gallons, you didn't say whether it was plaster, vinyl or fiberglass. Also, do you have a cartridge filter? If so, then that would explain the high CYA level since continued use of Trichlor without frequent backwashing can raise the CYA level quite quickly. Adding 2 ppm FC per day would result in an increase of 36 ppm CYA per month or over 200 ppm in just a single 6-month swim season. Evaporation and refill doesn't affect this at all since evaporation concentrates and refill dilutes right back to where you started, though adds to the pool whatever is in the fill water (typically TA and CH).

    Richard
    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"

  12. Back To Top    #12

    Join Date
    Jun 2008
    Location
    Marana, AZ
    Posts
    347

    Re: Treating a partially drained pool full of algae

    I live in a desert area. My CYA is a little under 40, and I have to add approx. 10 oz. of 10% liquid chlorine daily to maintain my levels in a 9400 gallon pool; I lose approx. 1 to 1 1/2 ppm daily. And my pool gets sun most of the day. In other words, a CYA of 40 is just fine for desert and other sunny areas.

    I have seen some CYA curves before, showing how much effect CYA has on chlorine burn off, but I would have to find the article again. Anyway, this article said that once you reach about 30 CYA, additional CYA has little affect on chlorine burn off. The same article said that it takes twice as long for chlorine to kill off a pathenogen at 100 CYA than it does at 50. Needless to say, I will not allow my CYA to get above 50!
    Above ground soft side Omega pool
    20 feet diameter, 4 feet deep
    Hayward sand filter
    Hayward 1 HP Matrix pump
    Hayward Aquabug Automatic Pool Cleaner

  13. Back To Top    #13
    JasonLion's Avatar
    Join Date
    May 2007
    Location
    Silver Spring, MD
    Posts
    37,879

    Re: Treating a partially drained pool full of algae

    Quote Originally Posted by Swimgirl
    I have seen some CYA curves before, showing how much effect CYA has on chlorine burn off, but I would have to find the article again. Anyway, this article said that once you reach about 30 CYA, additional CYA has little affect on chlorine burn off. The same article said that it takes twice as long for chlorine to kill off a pathenogen at 100 CYA than it does at 50. Needless to say, I will not allow my CYA to get above 50!
    That article is full of inaccurate information. Adding more CYA reduces your total chlorine consumption even though you have to raise your FC level to compensate for the less active chlorine. That continues to be true up to impractically high CYA levels, far higher than 50. Just follow the FC/CYA relationship and you are fine.

    There are other problems with CYA levels over 90, but they aren't the ones described in this article, which alternates between good information, misleading information, and just plain wrong.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
    Creator of PoolMath and Pool Calculator. Other handy links: Support this site, TF Test Kits, Pool School

  14. Back To Top    #14

    Join Date
    Jun 2008
    Location
    Marana, AZ
    Posts
    347

    Re: Treating a partially drained pool full of algae

    Quote Originally Posted by JasonLion
    Quote Originally Posted by Swimgirl
    I have seen some CYA curves before, showing how much effect CYA has on chlorine burn off, but I would have to find the article again. Anyway, this article said that once you reach about 30 CYA, additional CYA has little affect on chlorine burn off. The same article said that it takes twice as long for chlorine to kill off a pathenogen at 100 CYA than it does at 50. Needless to say, I will not allow my CYA to get above 50!
    That article is full of inaccurate information. Adding more CYA reduces your total chlorine consumption even though you have to raise your FC level to compensate for the less active chlorine. That continues to be true up to impractically high CYA levels, far higher than 50. Just follow the FC/CYA relationship and you are fine.

    There are other problems with CYA levels over 90, but they aren't the ones described in this article, which alternates between good information, misleading information, and just plain wrong.


    Listening to the wrong stuff, huh. I'm still learning.


    40 CYA is working very well for my desert pool, though. Chlorine loss is, like I said, 1 to 1 1/2 ppm.
    Above ground soft side Omega pool
    20 feet diameter, 4 feet deep
    Hayward sand filter
    Hayward 1 HP Matrix pump
    Hayward Aquabug Automatic Pool Cleaner

  15. Back To Top    #15
    Nick's Avatar
    Join Date
    Jun 2008
    Location
    Bristol, UK
    Posts
    36

    Re: Treating a partially drained pool full of algae

    If the pool hasn't been emptied and refilled for the past 20 years I would bite the bullet and go for a complete empty, scrub and refill. I'm assuming that you would use less chemicals that way and you could start fresh.
    Intex 16'x48" AGP 5,000 (uk) gallons
    Intex 635 pump
    Bio Diesel filter bags
    4 solar radiators and a solar cover

Posting Permissions

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