Slamming with high CYA - am I done?

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T

tradenet

0
May 30, 2015
8
Southern California
25,000 gallon in ground plaster pool, variable speed pump, DE filter. Currently using manual chlorination and acid using liquid chlorine and liquid muriatic acid. Recovering from excessive use of ch tabs by former pool guy.
Location, southern California.

Before I learned enough from this site to be confident in being able to manage my pool myself and send my pool maint. company packing, they had used pucks exclusively via feeder and though I had refilled the pool 2 years earlier, my CYA had increased to 150. I got tired of algae problems and their monthly fee made me think "with all these problems what am I paying for anyway?" This website helped me figure out what was going on and why typical chlorine levels weren't working.

I tried lowering CYA -- did some small partial drain and refills and also went through two separate does with 8oz packs of Bio-Active CYA reducer and then tried a 16oz pack of Bio-Active CYA reducer. I kept the FC level between 2 and 3 ppm for 10 days or more after each Bio-Active application. The water temps were between 72 and 78 while using the Bio-Active. From my measurements (4:1 dilution of pool water with RO water for the CYA test) the Bio-Active may have helped reduced the CYA level by 10ppm or so, but in general it has been ineffective. I plan on continuing with incremental drain/refills -- pumping the water onto the lawn and shrubs and disabling sprinkler system cycles appropriately to conserve water, to get the CYA down to less than 100, but was wondering what my target CYA level should be.

Separately, now and then I'd find a small bit of algae that I could easily brush off and decided maintaining low chlorine levels in the the hopes the the Bio-Active CYA reducer would actually work was a waste of time and was risky. I figured a shock/slam was in order.

Before Slamming numbers: FC 6, CC 0, TC 6, pH 7.5, TA 104, Calcium 630, CYA 130

Using what I think now was an outdated CYA/Chlorine shock table I read that 39ppm was a recommended shock level.

For all Chlorine tests I used the TF100 FAS-DPD chlorine drop test and the magnetic stirrer using 3 parts RO water and one part part pool water and multiplying result by 4 to speed up the test, conserve R-0870 reagent usage and avoid losing my mind by having to count out 80 drops of reagent. All measurements are FC, CC was always 0. If my reckoning on this testing method is incorrect, please let me know.


For all chlorine test results are FC, CC was always 0

The chronology of my slam follows:

Saturday:
9AM: - Pre slam FC = 6, TC=6. added approx 7 gallons of liquid chlorine and brushed pool

10AM: FAS-DPD test measured 40ppm (3parts RO water, 1 part pool water for FAS-DPD chlorine avoid having to speed up the test and conserve R-0870 usage), brushed again

12 noon: 26ppm chlorine - added another gallon of bleach after testing, brushed again
3 pm: 46 ppm chlorine (I must have screwed up the noon test), brushed again
5 pm: 44ppm chlorine, brushed again
8:45 pm: 34ppm chlorine, added another gallon of liquid chlorine after testing
10pm: 38ppm chlorine per test (last test of the day)

Sunday:
4:45 am (before sunrise) test measured 38ppm.

I see no evidence of algae in the pool, but this morning while perusing this site again and finding the pool calculator page, I noticed that for CYA at 130, it recommends
FC for shock: 51, FC for mustard algae: 69. Have I wasted a day and a lot of chlorine by slamming at too low a level of FC?

I'm now wondering if I should dump in another 6 gallons of chlorine and bump up the FC level to 70 for a day, or since there was no drop in FC overnight, conclude that I am done slamming?

If there were any algae, green or mustard (not sure how to identify the difference visually, but the bits I saw before the process seemed green) would the FC drop overnight even if I was only at an FC level of 38, or is algae so "tough" that no chlorine will be effective and consumed till I get the level to 70ppm at my CYA of 130.

I'd appreciate any suggestions as to whether I should continue with my current slamming cycle and escalate to 70ppm chlorine or, since there was no overnight drop in FC, I should consider the slam complete?

BTW, thanks for maintaining this most helpful and informative site and forums.
 
When you did your overnight test did you do it "normally" or with the RO dilution method you mentioned in your earlier testing?

For OCLT you should not use any dilution so that you can be sure it's as accurate as possible. :)

That's just my 2 cents.
 
Thanks Woodyp and Beens,

I used the Taylor "sample sizer" tool with the Taylor graduated cylinder to prepare one pool sample and three RO samples for each test. My final 10PM test and the re-dawn test used the exact same number of drops of reagent. Thus it would seem that if the test was not super-accurate in the absolute level of FC, it should be a good indication that there was no change if FC value overnight.

The water has been and is crystal clear.

My goal was to kill all algae so that I stop seeing small patches of algae that I have to brush off and keep my chlorine at 13 until I get the CYA down.
This site's article about slamming says it's not a one day process -- is it possible to be done in one day?

Also, I had used Pool School - Chlorine / CYA Chart to arrive at approx 40 for the FC target, but maybe I should have used the poolcalculator.com target of 69 to ensure that mustard algae spores, if present, would be killed. Would and FC level that got as high as 42 and remained above 30 for 18 hours do the job?

Lastly, should my target CYA be? I'll incrementally drain/refill to get there -- while using more water than a one-shot drain/refill I don't think the water will kill the lawn (I'll test on a small section first), but my lawn and shrubs couldn't handle 25,000 gallons in one shot.

Thanks again.
 
Thanks pooklv. The chart links you posted are a great reference. The fill water in my area starts with calcium at 325 so it's a constant battle to keep it from rising over time.
I'm in southern California where the summers are warm - generally 65-85 degrees, with a few days hitting 90. I've updated my signature accordingly.

Thanks again.
 
QRe: Slamming with high CYA - am I done?

pooklv,

I'm very grateful for your generous and expert assistance.

My FC level is ticking down after the slam, currently FC=29, CC=0. (I used a sample not diluted with RO water for max accuracy -- 58 drops of R-0871)

Currently I have concerns regarding being able to accurately measure pH, both when FC is at high slam levels and afterwards, if I keep FC in the range recommended by poolcalculator.com I'm pretty sure I read on this forum that it's difficult to measure pH at high FC levels.

Having a CYA level greater than 130 yields a recommended non-SWG FC level of more than 10 (7.5% * CYA is the rule of thumb I came across, poolcalculator.com says 10-16 FC).

Is there any way to measure pH properly at high chlorine levels?

In addition to the TF100, I have a ColorQ which correlates well with the TF100, except for cholrine tests -- both the TF100 chlorine drop test and ColorQ chorine samples turn cloudy -- the TF100 test can handle the cloudiness - the ColorQ cannot and it consistently overstates chlorine levels -- thus use the TF100 for most testing and only use the TF100 for chlorine testing.

BTW, I'm asked many folks, but nobody seems to know why the TF100 and Lamotte FC reagents turn the samples cloudy). I pretty much use the ColorQ only for pH since I'm never confident when trying to match color strips.

In any event, Lamotte says FC >10 might interfere with the ColorQ pH test resulting in a false high reading -- as a test I added the Lamotte reagent and tested in the ColorQ as rapidly as possible, attempting to take a reading before any negative impact of high FC might occur. I got a pH reading of 7.5 (same as my pre-slam reading and 0.1 higher than the week before. I let the sample sit for a few minutes and took another reading -- it had drifted up to 8.5.

Can I trust any pH test while my chlorine is till at high post-slam levels or afterwards if I keep the FC at 13 (mid-range) until I can get the CYA level below 130?

Are my other readings at risk of being false at high FC levels? My pre-slam TA was approx 95, currently it's at 93 -- seems to be steady.

My calcium seems to be around 630 most of the time. My pre-slam CSI was approx 0.25. I want to do all I can to prevent calcium scaling by keeping the water properly balanced and would appreciate any suggestions as to how to properly measure and thus manage water balance at required high FC levels until I can get the CYA down.
 

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You're welcome. You are correct with your concerns about testing PH. The Taylor/TF100 red PH test is not valid with FC over 10. None are that I am aware of. You will have to let your FC drop to 9 or 10 to test your PH, I would start with weekly and when you do lower PH to 7.2, or as low as you can without taking your csi out of range. We might need to work on lowering TA to help stabilize your PH and slow the rise if it does rise.
 
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