Advice about FC and CYA

[Brandoga]

Have been lurking TFP for several years, just joined the forum. Thanks for great results with TFPC. I mostly try to use bleach, but sometimes add Trichlor tabs when I'm away for a week or so. Pool has looked great all year. A friend was looking after the pool while I was away, noted low (or no) FC with OTO kit and dept adding four 3-inch trichlor tabs about every 5 days. FC wasn't coming up, so he went to pool store where they sold him PhosFree, told him to double-shock (with dichlor).
Yesterday I raised the FC to 20 with bleach; FC was 17 at 2 PM, 11 at 6 PM, and 4 first thing this morning. Latest test results:
FC 4
CC 0.5
CH 190
CYA 160 (50% dilution method with tap water. Now out of CYA reagent -- more should arrive from TFtestkits next week.)
TA 90
pH 7.4 (yesterday before I added the chlorine)

Went to local Leslie's looking for chlorine. (Surprised to find them using the Taylor K-2006.) They told me my CYA was 100, tried to sell me Bio-Active CYA reducer or recommended a water replacement. (Phospates - their test - <100 ppb)

Water is clear and sparkling, not sure why the OCLT shows such a drop. Pool water last night and this AM smelled like chlorine (unusual).
Here's my dilemma:
It would cost me about $300 to drain and refill, and there are about 6 weeks left in the season before I do a partial drain below the skimmers to winterize. (My CYA usually drops over the winter. Last complete drain was in 2009, to fix a crack.) Today I added 6.5 lbs Cal hypo 68% (on sale 50 lbs for $140) targeting FC about 25. Frankly, I'm a bit nervous about shooting for FC of 40-50 that the FC/CYA charts recommend, especially with water so clear, and smelling of chlorine already, I'm afraid to use the pool.

What I should do next? Keep the FC between 7-12? Keep the FC as high as I can until it passes the OCLT? Any other ideas?

Thanks, and sorry for such a long first post.

 

[singingpond]

I suppose you could run another OCLT to verify what you saw yesterday. However, if you've been using TFP methods for a while, you know that chlorine loss like you're seeing means a SLAM, which is pretty darn difficult at a CYA of 160.

Where was your CYA before your friend stepped in for the one week?

 

[Brandoga]

Sorry -- I was away for a while. Trichlor dosing went on for 2+ months. Hadn't checked CYA since I opened the pool in the spring, when it was 60. Also reluctant to drain, but I'm also going to have to buy a submersible pump to drain it down... (Also forgot to mention borates = 50)

 

[ping]

Welcome to TFP!

I'll start off by saying Bio-Active has proven to be a very big miss from most users here at TFP. Most of the positive results, very few, have been from new posters that have claimed success.

If it is worth the cost for a few more weeks of swim time by the time the pool has been refilled and slammed then I suggest replacing 75% of the water and following the SLAM process, see my signature. You need to decide to either pay now and enjoy the pool for the rest of the season or limp by and deal with it next year.

 

[Divin Dave]

Hi Brandoga,
Regarding the smell you are noticing. The smell is not Chlorine. The smell is Combine Chloramines which are a biproduct of the Chlorine oxidizing organics (likely algae), which is not yet visible which is evidenced by the large amount of free chlorine loss in such a short period of time. I suspect your CC is only.5 due to oxidation of the CC by UV. (lots of UV in Atlanta I suspect).

If your water is clear and no signs of algae, I would advise to raise the FC to SLAM level and keep it there for at least 1 day. If you catch it now, may well knock it out in 1 or 2 days. Check behind your lights, that may well be where the majority of it is. Light niches are famous for this type of thing.

I have a friend in the same shape as you are right now and we did this same thing with his. SLAMMED for a weekend and then keep FC at 11.5% of the CYA and hopefully will hold off a full blown outbreak until winter comes, when its more 'convenient'.

With my friends pool, this has been going on for about 2 weeks, and so far, successful.

I know this sounds sort of scary to have Chlorine levels so high. But is all based on science, and even so, it's difficult for most people to wrap their heads around. So, FWIW, here is a link to the science behind the madness of Pool Chemistry. Sometimes, even if you dont understand it, you have to trust it in order for it to all work out.
Pool Water Chemistry

 

[singingpond]

You may want to take a peek at this ongoing thread, particularly Chem Geek's comments on page 4 about managing a pool that has Phosfree, and is much more heavily overstabilized than yours. Partial drain is still a more straightforward solution to your problem, but the fact that you've used Phosfree, as well as borates (some algaecidal action), made me think of this thread
Rental Pool doesn't register chlorine - Page 4

 

[Brandoga]

Thanks for all the comments. I've read through Chem Geek's equations before (in the Deep End) and understand the science somewhat. If I read it right, his post yesterday on Rental Pool (thanks) suggests I might be able to inhibit algae with a slightly lower FC level, if I get ahead of the algae. Will I need to keep the FC >40 all weekend to SLAM it? (I should have ordered the big bottle of FAS-DPD drops.)

If I replace 75% of the water instead, I'd like to at least use the pool water for irrigation (it has been super dry here) but I don't want to kill the gardens. Do you know whether it would be sufficient to let the FC drop? If the CYA-bound Cl won't kill the algae, does that mean it won't kill the vegetables, either?

 

[chem geek]

You first need to get rid of the extra chlorine demand you are seeing. If you've got both low phosphates and 50 ppm Borates I'd be surprised if it's algae. Did the pool get to zero chlorine for a period of time (at least a day or more)? Do you have a pool cover or a solar system? You might take a look at your sand filter to make sure it's not channeled with biofilm. If it is, you can do a deep clean of it and use Ahh-Some for the filter.

As you note, a full SLAM would be a heck of a lot of chlorine (around 64 ppm FC), but why don't you try a half-SLAM to see what happens -- around 30 ppm FC or so. Just maintain that and see what happens with the OCLT. If it drops over time, you may be able to recover from this, albeit more slowly than with a full SLAM. Once things are stable, you can maintain 12 ppm FC as the regular FC/CYA level or if that is using too much chlorine (I don't think it will) you could try a lower FC level. The only reason I suggested the lower FC/CYA level for the rental pool was that it's CYA level was extraordinarily high so the normally required FC would likely freak people out (given it's a rental) and also to lessen the amount of chlorine usage since that was also an issue for that pool given its size.

 

[Brandoga]

Yes, pool got to zero chlorine when my friend went to pool store and got the PhosFree. He used it and 2 jugs bleach, kept the solar cover on. FC was zero again the next day, when I got home. I added three 121 oz jugs of 8.25% bleach, based on suggested FC levels (before I tested the CYA). The next afternoon it was down to zero again. That's when I tested the CYA and started amping up the bleach and cal hypo. 6 hours after cal/hypo today, FC is at 24 with solar cover on. (Does solar cover block UV?)

I don't know what "channeled with biofilm" is (or looks like). Filter deep-clean, like with a hose? I just learned about that on TFP yesterday. It will take me a couple of days to get Ahh-Some ($30 for 2 oz!). Is there any alternative? Sounds like I need to take care of this even if I do the water replacement.

 

[Brandoga]

P.S. When might it be safe to go in the water? I just retired from CDC, and it would be extremely embarrassing to get either (1) a flesh-eating bacteria or (2) chlorine burns.

 

[Divin Dave]

Its safe to swim as long as the FC is below the slam level of your CYA.

 

[chem geek]

I don't know what "channeled with biofilm" is (or looks like). Filter deep-clean, like with a hose? I just learned about that on TFP yesterday. It will take me a couple of days to get Ahh-Some ($30 for 2 oz!). Is there any alternative? Sounds like I need to take care of this even if I do the water replacement.

Yes, filter deep clean like with a hose. The Ahh-Some will be worth it IF your filter is clumped with biofilm. If your filter looks OK then wait since maybe the problem is with the solar cover. Feel the underside of the solar cover to see if it's slimy.

The days with no chlorine and the subsequent loss of CYA [EDIT] (wrong - why did I think that?) [END-EDIT] indicate bacteria may have grown in the pool so we need to find it and kill it. If the water is holding FC at all (which it is), then the bacteria are not in the water itself, but may be in chlorine-resistant biofilms on some surface. These aren't flesh-eating bacteria. Most likely they are Pseudomonas aeruginosa that is very common and readily forms biofilms. It's the bacteria most associated with "hot tub itch". If they are on the cover and you take the cover off, then you should be fine in the pool water. If they are in the filter, then it's possible some may slough off out of the filter, but with intact skin you're less likely to be affected. This bacteria is more of a problem in spas because one's skin pores are opened up more in the hot water so are more susceptible to getting overwhelmed by bacteria. Also, spas tend to go south more frequently and faster than in pools because of their higher bather load (more nutrients in the water) and hotter temperatures (faster growth rates).

 

[duraleigh]

It would cost me about $300 to drain and refill,

In most places in the US, water rates are around $5/1000 gallons. If your rate is near that, you can drain 20k for $100 and simplify your life.

 

[chem geek]

See Is Atlanta drowning in the nation's highest water bills? and Water & Sewer Rates and this link. The most likely marginal rate beyond 3 CCF (2244 gallons) is $6.16/CCF which is per 748 gallons or $8.24/1000 gallons.

Though replacing your water will get your CYA level lower which definitely will make pool maintenance easier, it won't get rid of biofilm on your pool cover or in your filter if that turns out to be the source of your chlorine demand. Nevertheless, you'll be able to SLAM more easily without needing as much chlorine so water replacement could still be the least expensive way of getting your water into shape.

 

[Brandoga]

Rates here for 20K gallons: $65 water, $245 sewer. Welcome to Atlanta (where we need to raise money to fix the sewer system so untreated water doesn't keep flowing down the Chattahoochee to you guys in FL.)

Solar cover is squeaky clean - no slime. Deep cleaned the filter - no clumps, surprisingly little dirt, some cloudy particles. Removed the pool light: ribbons of gelatinous grey stuff floated out, slowly sunk to bottom. Yuck. Vacuumed the light niche and stuff off the bottom to waste. (Tried to catch some in a net, to look at under a microscope, maybe do a gram stain -- no luck. Just dissipated.)

Didn't test after the 6.5# cal hypo this morning; FC was 21 at 2:30 PM, 18 at 6:30 PM (titrating a measured 5 ml, 'cause I'm running low on the drops). Added another 4# cal hypo, running the Polaris to stir it up, hoping to get FC over 30 to half-SLAM, per Chem Geek's advice. Will see what happens with the OCLT tonight.

Really appreciate all the expertise and advice. I'm gratified by the number of sage responses I received within 6 hours of my first post, and, as a geek myself, especially appreciate Richard Falk's detailed, scientific explanations. (Italics for Pseudomonas​ even.) I might end up changing the water anyway, but sorta glad I found that gunk behind the light. I'll check in tomorrow. -Bernie

 

[chem geek]

So maybe you got lucky and the chlorine demand was just some bacterial growth, maybe some partial degradation of some CYA (though you didn't see a drop), and that you just need to oxidize through that with chlorine. Certainly cleaning behind the light niches will get rid of other sources of chlorine demand, but those aren't usually that high because not much water flows through such niches. Crossing my fingers for you.

 

[Brandoga]

Well, FC was 24 last night, 18 this AM, pool's uncovered. CYA is 100-110 (can't repeat it again until new reagent arrives this week), CH 260. A little cloudy (maybe from all the cal hypo?) Adding 8.25% bleach today, hoping for the best.

 

[pabeader]

Rates here for 20K gallons: $65 water, $245 sewer. Welcome to Atlanta (where we need to raise money to fix the sewer system so untreated water doesn't keep flowing down the Chattahoochee to you guys in FL.)

Solar cover is squeaky clean - no slime. Deep cleaned the filter - no clumps, surprisingly little dirt, some cloudy particles. Removed the pool light: ribbons of gelatinous grey stuff floated out, slowly sunk to bottom. Yuck. Vacuumed the light niche and stuff off the bottom to waste. (Tried to catch some in a net, to look at under a microscope, maybe do a gram stain -- no luck. Just dissipated.)

Didn't test after the 6.5# cal hypo this morning; FC was 21 at 2:30 PM, 18 at 6:30 PM (titrating a measured 5 ml, 'cause I'm running low on the drops). Added another 4# cal hypo, running the Polaris to stir it up, hoping to get FC over 30 to half-SLAM, per Chem Geek's advice. Will see what happens with the OCLT tonight.

Really appreciate all the expertise and advice. I'm gratified by the number of sage responses I received within 6 hours of my first post, and, as a geek myself, especially appreciate Richard Falk's detailed, scientific explanations. (Italics for Pseudomonas​ even.) I might end up changing the water anyway, but sorta glad I found that gunk behind the light. I'll check in tomorrow. -Bernie

Since you won't be putting the water in the sewer, that charge goes away. All you need to do is tell your utility what you are doing and they prorate based on the actual usage.

 

[Brandoga]

So replaced about 1000 gal of water,kept the FC above 30 for a couple of days, over 20 the last 2 days, and we got about 3 inches of rain. FC was 11 last night. This morning FC was 9. Added 1 jug 8.25% bleach

FC 14
pH 7.4
CH 250
CYA 80 (straight, and repeated twice w/ 1:1 dilutions, new reagent from TF-100).

Is this believable? Can I let the FC run in the 6-9 range now? Thanks for advice.