How long to pass oclt after yellow mustard?

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adpaul3

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Jul 20, 2012
6
Indianapolis
First off I want to say that this is a great forum and website. I've learned quite a bit from reading this forum and pool school.

Backround; pool and equipment are 9 years old. I purchased this house a month ago and have never owned a pool before. I expected a learning curve but everything went too smoothly at first. The pool was opened the begining of June by a pool professional. The pool was covered and the pump was running 24/7 until 6/24. 6/15 was the first time the pool was used and it looked great. 6/23 moved in and the pool has been used ever since. The pool is covered when ever not in use. Using the basic test kits for readings I added chlorine sticks to keep the level around 5 ppm. I had the water tested at a local pool store and was told everything was fine except for PH at 6.8 and CYA at 170. I was told to monitor cya to see if the results would remain the same and add PH up to increase Ph to 7.2. I adjusted the PH and ordered a TF-100 test kit.
7/13 first test PH 7.2, FC 5.5, 0 cc, TA 150, CH 170, CYA 100. I wish I knew then what I know now. Pool is still perfectly clear.
7/14 Added Algaecide as a preventitive measure. I used Dupont's dimethly benzyl ammonium chloride. I didn't know of polyquat 60 then.
7/15 In the evening the pool was not as clear as normal
7/16 Opened the pool to see it cloudy and had 0 FC. I started reading more here, added 9 gallons of 6% bleach and closed the pool. When I opened it in the evening yellow algae was floating on top. Added more bleach to reach regular shock levels.
7/17 By the end of the day the pool was back to being cloudy with no vissible signs of algae. In two days I had used 34.5 gallons of bleach. I wish I had pumped out half the water in the begining of June to have a manageable cya.
7/18 and 7/19 Chlorine continued to be consumed but at a lesser rate. I used 9 gallons of 12.5% clorine trying to maintain FC greater than 25 on theese 2 days. My cc consistently held at 1ppm. The water looked pretty good by the end of Thursday.
7/20 My oclt was 10 (31 down to 21). I added DE to my sand filter, ran it a couple of hours until skimmer flow was low, back flushed and repeated a second time. By the end of the day I added water, used 3 gallons of 12.5% chlorine and the pooled looked great but ...
7/21 oclt was 7.5 (31.5 down to 24) The water test result first thing were PH 6.8, FC 24, CC 0, TA 180, Ch 170, CYA 90
7/22 Still at shock level. 3 gallons of 12.5% added
7/23 oclt at 3 (26 down to 23) cc at .5. 2 gallons of 12.5% added through the day. Pool looks beautiful and feels squeaky clean.
7/24 Oclt at 3 (26.5 down to 23.5) cc at .5. I removed the light to find some dead algae behind it. Other than that everything looks and feels great great.

My question is this, How much longer should it take until my oclt is below 1 and should I go to the mustard algae shock of 49 now? I have not raised the PH yet because I would like to lower my TA and add borates.

Any help or comments would be appreciated. Sorry for a long first post but I didn't want miss anything. Also pool temps have been 89-96 during my problem.

Thanks,
Paul
 
Welcome to tfp, adpaul3 :wave:

What test kit are you using to get your numbers?

Ph tests are not valid above when the FC is above 10 ppm. I would let your FC drop briefly below 10 ppm now and retest ph, then adjust. It is likely very low right now. Get it up to 7.2 (again testing when only below 10 ppm FC).

From what you shared (nice job by the way on your log), you cya is high and should be reduced soon. The only common way to do the is by partial drain/refill. Unless you have a Saltwater chlorine generator (swg), you want to shoot for 50 ppm cya.

Why do you think you have mustard algae? Nothing you have wrote makes me think you do...it sounds more like "normal algae". See: http://www.troublefreepool.com/pool-school/mustard_algae

Either way, deal with ph now...then until you pass the OCLT, I would keep at normal shock levels. I would also recommend lowering cya asap.
 
Thanks for the quick reply. I am using a TF-100 test kit. The algae that was floating on top on the evening of 7/16 was a yellow-brown so i assumed it was mustard algae and not green. It is definitely not pollen. The pool is covered by an opaque power cover and only a few surrounding plants. My plan was to
1) Resolve clorine consumption problem
2) Lower FC to 10 and adjust PH with Borax
3) Buy time until the kids are back in school (3-4 weeks) then drain 50% of water and refill.

You are recommended taking care of PH first and then FC? I thought Chlorine was more effective at a lower PH. Would using borax to raise PH be a bad idea with my TA at 180?

Thanks
 
adpaul3 said:
You are recommended taking care of PH first and then FC?
Click to expand...
Yes, I think your ph might be quite low, especially if you have adjusted it while above 10 ppm FC. I would let it drop down briefly and check it, then get it up at least above 7.0 (but no higher than 7.4).

I am not very experienced on Mustard Algae...were you seeing it on the wall in the shaded portions of your pool?
Going up to 49 ppm FC will take a bunch of chlorine, so if you are able to pass the OCLT and you can get it up to 49 for 24 hours...it may work, but I am not sure I would bet on it. Either way, once you are done with the shock process (pass the OCLT, CC<0.5, 24 hours at MA levels, pool clear), I would suggest keeping your FC above the "Yellow Mustard Minimum" for the rest of your season, this value is here: http://www.troublefreepool.com/chlorine-cya-chart-t2346.html#p18157.
 
I should have been clearer. I adjusted my PH from 6.8 to 7.2+ around July 10th when my FC was around 5.

I never really noticed anything on the vinyl because the water was so cloudy. The only direct evidence was the gooey yellow brown stuff on the water. At that point I raised the FC to above regular shock levels and ran the pool cleaner(Polaris 9300).

I agree that I should keep FC above 13.5 for the rest of the year.
 
adpaul3 said:
I adjusted my PH from 6.8 to 7.2+ around July 10th when my FC was around 5.
Click to expand...
Seeing your reading of 6.8 has me a bit worried, since you ph should read high (not low) at high FC levels. You haven't by chance used trichlor pucks or dichlor shock during the process? Both of those lower ph.
 
I did use some Aqua Chem Dichlor on either 16th or 17th since I was out of bleach and I didn't want to drop below FC shock levels. I believe I used 11 pounds as per the pool calculator. Should I use Soda ash or Borax to raise PH, Keeping in mind I would like to add borates at a later date.

Thanks again for all the advice,
Paul
 
Yep, that amount of dichlor would drop quite a ways (and part of the reason we do not recommend shocking with it or trichlor). It might be best to let it fall and check the ph sooner then later. I would use borax to raise.
 
Thanks, I will let the FC fall and buy Borax tomorrow. I have another question will aerating the water at night influence anything other than PH? i.e. Does any other pool chemistry evaporate off or is easily change by more air exposure?
 

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