FC dropping 10ppm/day - I can't keep up with it!

[RecurveArcher]

Here are current test results; pretty much everything stays exactly the same, all the time, except for FC:
- pH: 7.5
- FC: 40.0
- CC: 0.5
- TA: 190
- CH: 325
- CYA: 110
- Bor: 30

Based on FC vs. CYA chart, our minimum FC should be about 8, target 13, and shock 43 (house purchased last year, CYA still really high from previous owner and me using the rest of the tablets they left behind - currently use 100% liquid). One gallon of the 10% chlorine bleach from Walmart usually increases FC by about 3ppm. We leave it covered all the time, so water and FC loss is usually very minimal.

----- Long Story -----
A few weeks ago we found the pool just slightly cloudy one morning, not bad, but not as clear as usual. I happened to have tested the water the night before and did again in the morning when we found it cloudy, and FC had dropped from 14 to 7 overnight.

So I add 12 gallons of bleach to shock it… Test again later that night once it’s had a chance to circulate and it was at 42.5 and water was clear. Test again the next morning and it’s down to 36; must not have gotten it high enough…

I add the last 3 gallons I have on-hand, should take it to 45ish, go get 10 more gallons from Walmart the next evening, test again, and it’s down to like 30. I add in 8 gallons, figure that’s sure to get it high enough.

Meanwhile, the cover rope breaks, I order parts but they’re going to be a week, I can still manually open and close but it’s a PITA, and I have to travel for work for a few days anyhow, but surely the FC got high enough with the 8 more gallons (8*3=24+30=54!!). So it’s about 5 days before I test again and FC is at 16…

I go back to Walmart, buy 20 more gallons, put 14 in the pool (14*3 = 42+16=58!), but I test it the next morning and FC is at 42. I put in the other 6, test again this morning, and FC is at 46. I test again tonight, almost exactly 12 hours later, and FC is at 40.

-----Short Story -----
I’m now burning through about 10ppm/FC/day (have gone through 40+ gallons of chlorine in ~ 3 weeks) and either shocking the pool isn’t working (could that be?) or I’m unable to get it to (and maintain) the shock level. It seems like I’m getting diminishing returns on FC increase per gallon of chlorine as it gets super high; either that or it’s eating away at it crazy fast, but I can’t keep up with it.

----- Questions -----
I’m guessing the answer is that FC is dropping so fast that I haven’t been able to maintain the necessary level for long enough, or my CYA is a lot higher than I think and I’m not even getting it to shock level in the first place, but my CYA is basically the same, maybe even a touch less, than it was last year. Last year I did have to shock it once, had very obvious algae, FC dropped to 0 (from ~ 15) is less than 2 days, I got the FC to 42 in one go and it cleared up overnight, that was that (took almost 2 months for the FC to get back down to the low teens). This time the water was just barely cloudy for half a day and since then it’s been clear, but I’m dumping massive amounts of chlorine into the pool and running the robot vac a couple times per day on most days. The filter pressure went from 15 to 16 on the day that it was cloudy, and then dropped back down to 15 in a few days and has stayed there since. I’m about done with it, ready to let it sit until next year and deal with it then.

Assuming the wife gets me to deal with it now, what do I do? Should I just dump in like 30 gallons of chlorine at once - guarantee that I get it high enough? At a drop rate of 3-4 gallons/day I simply can’t test it often enough to make sure I’m maintaining shock level, so I don’t see another option. And how high do I go? I’ve added enough twice to get the FC to what should have been about 60ppm! Is there something else I can try shocking it with?

I’m guessing option B is to drain some of the water so that I can bring the CYA down, but the floor drain doesn’t work and my cover pump would take a month to pump out any reasonable amount of water. I also don’t have a fence, so I can’t leave the cover open unattended, and I’m on well so I’d need to ship in water, which would cost a whole lot more than 30 gallons of chlorine (estimate about $1200 to fill the whole pool).

Either way, what could possibly be causing this kind of FC loss with clear water? And not dying with FC at 60 ppm? Could there be something in the plumbing somehow that’s a constant source of contaminant that shocking the water isn’t able to get rid of?

As always, thanks for the help.

 

[mknauss]

I assume you tested the CYA by diluting with tap water 1:1 and then doubling your result. Also doubles your error rate so could be as high as 130.

Pretty much impossible to SLAM with this high of CYA. Up to you but I assume you drain some for winter and thus you could continue what you are doing to limp along and have ugly water or bite the bullet, rent a sub pump, and bring in the water truck.

Take care.

 

[jblizzle]

Admittedly I only skimmed the long post

Are you following the SLAM Process process?
Know that the higher your FC level above the maintenance level, the more ppm of FC you will be losing. If you are at 40ppm, it is reasonable that you could be losing 10-15ppm of FC each day just to the sun.
It will never stabilize at the shock level.

Remember there are only 2 things that consume the FC, the sun and organics in the water.
Have you performed the Overnight Chlorine Loss Test to see if there are organics left in the water?

It also seems like you are just blindly adding a lot of bottles of FC. You should be just targeting your shock level in PoolMath?

 

[RecurveArcher]

I assume you tested the CYA by diluting with tap water 1:1 and then doubling your result. Also doubles your error rate so could be as high as 130.

I have not done it this way (should I try that?); I've followed the directions on the test kit (fill to bottom of label, solution to top). 100 is the highest the meter goes, but the dot goes away just before it gets there.

Admittedly I only skimmed the long post

Are you following the SLAM Process process?
Know that the higher your FC level above the maintenance level, the more ppm of FC you will be losing. If you are at 40ppm, it is reasonable that you could be losing 10-15ppm of FC each day just to the sun.
It will never stabilize at the shock level.

Remember there are only 2 things that consume the FC, the sun and organics in the water.
Have you performed the Overnight Chlorine Loss Test to see if there are organics left in the water?

It also seems like you are just blindly adding a lot of bottles of FC. You should be just targeting your shock level in PoolMath?

Long, I know, sorry. Short answers:

Trying to follow the SLAM process but OCLT is dropping about 6ppm overnight. Pool stays covered so typically (even at very high FC ~ 42 last year) I lose less than .5ppm/day. I do use the poolmath; that and based on experience 1 gallon typically increases FC by about 3 ppm. And yes, I'm now somewhat blindly throwing in more and more because no matter what when I test ~ 12 hours later FC is way lower than I'd expect it to be.

mknauss kind of alluded to another possibility that I'd thought of, that the CYA is literally so high that it can't be shocked; is that possible to get to a level that no matter how much chlorine you add, it won't have the shock effect?

 

[jblizzle]

You can always get the FC level up to shock level, but with very high CYA level, the FC level just gets ridiculous.

6ppm loss overnight is on the high side and seems to point to something in the water.

I agree you should try the diluted CYA test and see what that says.

 

[RecurveArcher]

*** Update ***

I did the diluted CYA test (3 times) and got pretty much the exact same result (55*2=110); if anything, I might say it indicated a slightly lower CYA (dot visibility varied a little depending on where exactly the light was).

I also started using this method to test the chlorine as I'm going to insane amounts and going to run out of solution; I assume this is okay (understand there is a bit more error variance).

So... I got some more chlorine and here are the test results from my original post and each test since then (again, for reference, typically 1 gallon of chlorine will increase my FC by just over 3ppm, and target shock level for my CYA is 43):

Date/Time - pH - FC - Added
------------------------------------
7/20 7:40 PM - 7.5 - 40 - N/A
7/21 6:39 PM - 7.9 - 35 - 15 Gal Chlorine
7/22 8:43 AM - 8.2 - 59 - 1 Gal Acid
7/22 12:11 PM - 7.9 - 59 - N/A
7/22 8:08 PM - 8.3 - 49 - 5 Gal Chlorine & 1 Gal Acid
7/23 8:54 AM - 7.9 - 54 - N/A
7/23 8:07 PM - 7.6 - 57 - N/A

So I added a bunch more chlorine up-front to make sure an get it above shock level, and keep it there long enough until I was able to test again. Adding 15 gallons when already at 35 I'd expect it to go to ~80, but it was only 59 the next morning, but the pH had spiked as well. You can see the results, but since then the pH has been up and down, but seems to have stabilized now, and the FC has actually gone up from this morning (or at least not dropped considerably), so that's promising.

Question: As I understand, higher TA will make the chlorine less effective (maybe how I ended up with problems in the first place, high TA + high CYA); I didn't test the TA as the pH increased, but assume it went up as well. Would a change in TA/pH change the measured FC level? I'm just wondering about the measured increase (and did the test twice) between this morning and this evening; is it pH changes, testing error/variance, or could it be something else?

I will test again in the morning and see if the FC continues to stay up.

 

[mknauss]

Oh my, why did you not drain some water? You have a number of potential issues going on.

Your pH is not accurate at all at a high FC. Your TA has no effect on the chlorine. A low pH does help the effectiveness of chlorine.

I really encourage you to drain at least half of your water and start over. There are many pitfalls in trying to do this like you are.

Take care.

 

[GoGrabTheNet]

I'm jumping in on this one to say that some water should be drained. The evil yet beneficial CYA is quite high, thereby hampering your results.

Also, how clean is that cover you keep on your pool? Could there perhaps be some organics and/or algae that could be colonizing on the bottom side or leaching into the pool?

Furthermore, what bleach are you buying from Walmart? I didn't know Walmart sold the 10% kind. Are you buying the 2-pack boxes like what's sold at Home Depot or Lowes? If so, then that is the KemTek brand "chlorinating liquid," and it is absolutely imperative that you buy boxes that have the most recent date codes.

At this point in time, the freshest date codes on the boxes near me are 2017:188. The second number is the Epoch Calendar day. So, that's a little over 2 weeks old. Still powerful stuff. In fact, I think they actually make the solution closer to 12% to compensate for shipping and storage losses.

 

[RecurveArcher]

Oh my, why did you not drain some water?

I 100% get that's the best solution, but the pool needs some work (rust patching, acid wash, repainting, coping replacement, etc.), and it's going to have to be drained to have it done. I'm not willing to drain half and pay to to have it re-filled, just to drain it again within a year to have the work done, and my wife didn't want to close it down for the season yet.

Also, how clean is that cover you keep on your pool? Could there perhaps be some organics and/or algae that could be colonizing on the bottom side or leaching into the pool?

It's a top-mount automatic safety cover, so attached to the pool deck. The only time you see the underside is when it's opening and rolling up on the reel. It's not super clean, but I've not noticed any obvious algae on it either. I kind of assumed that since the bottom was touching the pool surface (for the most part) that the chlorine would keep it bacteria free as well, but maybe not? Is introducing contaminants a common issue for covers? Since it's not easily removed, is the best way to clean the underside, just little-by-little on the reel while opening it a little at a time?

Furthermore, what bleach are you buying from Walmart? I didn't know Walmart sold the 10% kind. Are you buying the 2-pack boxes like what's sold at Home Depot or Lowes? If so, then that is the KemTek brand "chlorinating liquid," and it is absolutely imperative that you buy boxes that have the most recent date codes.

It's labeled as Pool Essentials (https://www.walmart.com/ip/Pool-Essentials-Chlorinating-Liquid/48938023). I live in-between two Walmart stores; one only carries them by the gallon, the other does sell 2-pack boxes as well. Even if labeled differently, might still be the same stuff. I'd not thought about checking dates, usually I just load up the cart and check-out. What time frame is acceptable (e.g., last 30 days)? And how long can it be stored (usually keep extra's in the garage or pool house - no direct sunlight)?

 

[RecurveArcher]

Morning update - I just tested pH at 7.5, TA at 150 (down from original 190), and FC at 57 (same as last night and same/up from yesterday morning).

I'll give it another day or so, but hopefully it's done now...

The water is a little low, so if there's no more FC drop tomorrow I can top it off. I'm not comfortable trying to fill the whole thing (or half) from the well, but I don't mind doing top-offs (I soften and filter the line that runs to the pool house). We've had a lot of rain this year, so I can try to drain a little every few days and keep topping it off gradually to try and bring down the FC and CYA levels little by little.

I'll also try to borrow a pressure washer and clean the under-side of the cover, just in case.

Two more questions:
1) Last year when we had an algae outbreak the FC tested at 0 when we found the pool cloudy; it'd been 2 days since I tested but the last test had it at 16. This time it tested at 7 when we found it cloudy and I had tested the night before at 14. So considering that, with the cover on and no use, the FC typically drops less than .5/day, both times the FC should have been above our target level when something happened that started to consume the chlorine very quickly. Is that normal, or any ideas of what could cause it? Pretty much everything on here says that keeping the FC balanced should prevent issues, but that doesn't seem to be the case for me.

2) We are planning to install a SWG after we do the pool repairs (which maybe could resolve this issue itself if it's caused by the exposed rust or plaster?); I'm curious if a SWG would be susceptible to the same issues (a very quick drop in chlorine, even when balanced) - i.e., would it be able to keep up with the high short-term demand?

Thanks again for all the help,
Sean

 

[AftonJeeper]

First, don't waste time/reagents testing pH when FC is over 10, it will be a false reading.

1) Yes, anything outside of your normal demand could be an outbreak. I have an auto cover and use less than .5ppm per day when not in use. Lost 4 over a 2 day period of no use and water started to turn cloudy, took 2 days to get back to clear.

2) SWG are great at maintaining FC, if there is a demand for more you need to make adjustments.

I'd recommend calling a couple well companies around you. My well company told me to run the well non stop so the pump wasn't turning on and off. It took 3 hoses to keep mine from shutting off. 40k gallon pool filled last year, well is now 20 years old. BTW, Trucking water in to fill my pool and the cost of a new well pump were not too far apart.

 

[Akathisia]

...I'm curious if a SWG would be susceptible to the same issues (a very quick drop in chlorine, even when balanced) - i.e., would it be able to keep up with the high short-term demand?...
Sean

Short term high FC demand will need to be met with bleach. SWG is great for maintaining levels and if you keep FC at the target (higher) end with regular testing you should have no problems.

 

[jblizzle]

Your pH might be very low right now since when FC is greater than 10ppm, the pH reads artificially high.

 

[PAGirl]

Short term high FC demand will need to be met with bleach. SWG is great for maintaining levels and if you keep FC at the target (higher) end with regular testing you should have no problems.

First, don't waste time/reagents testing pH when FC is over 10, it will be a false reading.

1) Yes, anything outside of your normal demand could be an outbreak. I have an auto cover and use less than .5ppm per day when not in use. Lost 4 over a 2 day period of no use and water started to turn cloudy, took 2 days to get back to clear.

2) SWG are great at maintaining FC, if there is a demand for more you need to make adjustments.

I'd recommend calling a couple well companies around you. My well company told me to run the well non stop so the pump wasn't turning on and off. It took 3 hoses to keep mine from shutting off. 40k gallon pool filled last year, well is now 20 years old. BTW, Trucking water in to fill my pool and the cost of a new well pump were not too far apart.

7th 9