Very High FC Depletion from Sunlight - How'd my CYA drop?

[RoberTX]

Hi,

My pool FC has been dropping 10 ppm daily due to sunlight. CC is always zero and I verified an overnight chlorine loss of less than 0.5 ppm (dropped from barely 14.0 to 13.5 from 10:45 pm to 6:30 am).

So I tested everything last night and this is what I got.

FC 3.5
CC 0.0
pH 7.9..8.0
TA 110
CYA less than 30 dot barely visible with tube filled to rim
CH 260

I immediately added 3 168 oz jugs of 6% Bleach. Adding $8 worth of bleach every night is getting old fast! :grrrr:

This morning I added about half a gallon of 31.45% Muriatic Acid. I over compensated a bit and now the pH is 7.2..7.3. My pH tends to drift up about 0.3 per week, so I plan on letting it rise on its own as opposed to adding soda ash (or similar).

I remeasured CYA (didn't know if the previously high pH affected the low CYA reading) and it was still the same (under 30).

So... I have tons of dichlor and 3" tabs as I have only recently converted to the BBB method. Should I add 3-4 lbs of dichlor and leave tabs in the floater until my CYA is up? Or should I buy stabilizer?

I'd really like to know why my CYA dropped so much. In June I replaced half my water to lower the CYA from 95 to 50. So it's been about 45 days and my CYA has really dropped. There has been a fair amount of splashout and I had to drain several inches from a few rains, can that account for all of this CYA loss?

Please advise if dichlor/tabs are appropriate for raising the CYA over the next week or so. If my CYA is going to be dropping 20 ppm / month, I may as well go back to the (much easier) tab chlorination. The reason I switched to bleach was to avoid my CYA reaching 95 as it did before.

 

[svenpup]

CYA usually drops slowly due to splashout.

Over the winter there are reports that CYA is metabolized by bacteria into ammonia, but this only occurs when FC is at 0 for extended periods which doesn't apply here.

Do you have an autofill? A leak masked by an autofill would present like this.

 

[RoberTX]

My pool is 'auto-filled' because I leave my valve slightly cracked and water drips slowly throughout the day. It's just enough to keep up with evaporation. I doubt it could be masking a leak, but I suppose it's possible.

Any advise on how to correct the CYA for now?

Thanks,
Robert

 

[Melt In The Sun]

Dichlor is fine for now. Just turn off your autofill and see if your level drops.

Have you done a lot of backwashing?

 

[RoberTX]

No backwash since the CYA was measured in mid-June. I will shut off the auto fill and see if the level drops more than a normal evaporation amount.

I put the floater in the pool with 3" tabs, and I'm going to add 3-4 lbs of dichlor tonight and tomorrow night. I'll then check the CYA again. According to poolcalculator 8 lbs of dichlor will raise the CYA by about 18.

BTW, my CYA regent is getting low, what is the best to replace just that one regent? The rest of my Taylor kit is still good.

With any luck when my CYA is up to about 40, I can add 1 jug (3 ppm) a night instead of 3 jugs (9 ppm) every night.

Thanks,
Robert

 

[Beez]

I put the floater in the pool with 3" tabs, and I'm going to add 3-4 lbs of dichlor tonight and tomorrow night. I'll then check the CYA again. According to poolcalculator 8 lbs of dichlor will raise the CYA by about 18.

I would do the math and figure out what is most economical: Pucks & dichlor vs. stabilizer granules.

But if I were in your shoes, I would want some CYA in there pronto. To me, that means add stabilizer granules immediately.

 

[RoberTX]

Well I just added 3 lbs of dichlor, and that should raise CYA by 6.7. I was just barely under 30, so I am going to add 4 more bags tonight, which should raise the CYA by 16 in all. That should get me somewhere around 35-40. I'll test all levels again tomorrow morning.

Still open to suggestions though :-D

Robert

 

[zea3]

Last season my CYA was 90. I drained below the return for the winter and in the spring when I refilled the CYA was 70. Had a huge rain in early June that put 6+ inches into the pool. I don't know how much water was "overflowed" out of the pool but my CYA dropped to 50. Had another big rain in mid June that did the same thing and my CYA is now around 35-40. I think the lower the CYA the more it dilutes in a drain and fill situation. Last season I did several drain and fills to get the pool down to 90, draining about a 1/3 of the pool each time.

So the gist of this post is yes, when CYA is already mid to low range, an overflowing rain can have the same effect as a partial drain and fill to lower CYA. If you had bacteria eating your CYA you would be seeing other symptoms as well, I think.

 

[duraleigh]

RoberTX,

I'll test all levels again tomorrow morning.

That won't work. It will take at least 2-3 days and sometimes as long as a week for CYA to register on the test.

I suggest you calculate the remainder of what you need to get your CYA up to 50 (I would assume you had 15 when you did the test) and put that amount in your pool in the form of CYA granules.

I personally think di-chlor is troublesome in that it raises the CYA too slowly or FC to fast, depending on how you look at it.

It's your call on what you use to raise it but the important thing is I don't think you had as much (nearly 30) as you thought and you are adding it too slowly with dichlor to get to 50ppm which I would want to do as quickly as possible.

Disregard the bacteria issue.....your pool doesn't have the conditions for that. I would suspect the autofill.....they can be pretty insidious.

 

[RoberTX]

OK, I'm off to wal-mart to buy some of that HTH CYA and some nylons .

I'm thinking I'll add the entire four pounds. Assuming my CYA is 15, they 4 lbs of stabilizer should increase CYA by 18, and the dichlor should have raised it by 9, so my total in a week should be about 40..50.

 

[duraleigh]

That sounds like a good plan. I assume that TX on the end of your username is for Texas so don't hesitate to get closer to 50ppm CYA than 40ppm in that latitude and climate.

 

[Beez]

That sounds like a good plan. I assume that TX on the end of your username is for Texas so don't hesitate to get closer to 50ppm CYA than 40ppm in that latitude and climate.

I actually took mine up to 60...

 

[RoberTX]

Would the advantage of targeting a CYA of 50 (or 60) be? less use of bleach? FC would deplete less due to sunlight and the target FC is 7 for a CYA of 60. So, what is the downside? With a higher CYA will it take more bleach to raise the FC by 1 ppm? If not (assuming you never need to shock) what would the disadvantage of using a CYA of even 70 be?

 

[svenpup]

Would the advantage of targeting a CYA of 50 (or 60) be? less use of bleach?

Yes

FC would deplete less due to sunlight and the target FC is 7 for a CYA of 60.

Yes

So, what is the downside?

It is difficult to shock if you ever let FC slip and need to.

With a higher CYA will it take more bleach to raise the FC by 1 ppm?

Nope

If not (assuming you never need to shock) what would the disadvantage of using a CYA of even 70 be?

That's it; if you have to shock it is more difficult.

 

[duraleigh]

what would the disadvantage of using a CYA of even 70 be?

sven already answered.....it's like aspirin, two is good for you, but 6 is not.

Everything gets more difficult to contend with if you have a manually chlorinated pool over 50-60.

 

[RoberTX]

I've been thinking more about this... If there is a leak, how did my CH increase from 220 to 260? I haven't used ANY chlorine sources other than bleach since mid-June, when my CH was 220. My tap water CH is 120. So if I had a leak substantial enough to lower my CYA from 50 down to ~15, then wouldn't the CH be expected to have decreased to somewhat, as opposed to rising by 40 ppm?

Basically, my CYA reduced by 35 ppm ( 70% :!: ) in 45 days... That leak would have had to cause my water to be replaced by 70%. That would have caused my CH to reduce to around 150 (I guess).

I've been reading this post and this post - it sounds like high temperatures and high pH can cause increased oxidation of CYA by chlorine.

We've had 100+ highs almost every day and lows haven't been getting below 80. I've also been busy, and have allowed my pH to sit b/w 7.8 and 8.0 for over a week. Maybe that is (at least partially) the cause. Combine that with a rainy June and a reasonable amount of splashout (cannonballs) and it's still hard to explain a CYA loss of 70 pph(%). However, if you factor in the tolerance in the CYA measurement.... :blah: :blah: :blah:

Robert

Any thoughts?

 

[duraleigh]

Your CH result is a valid point and would seem to eliminate the autofill for sure.

chalk it up to experience. There are a lot of variables in pool management. We take out many of them through accurate testing and dosing but, even then, there can be combinations of errors that simply don't produce the results we suspect.

The important thing is to get it in there now so you can reduce your chlorine demand and get your pool back to normal.

 

[geekgranny]

Howdy neighbor. Over here in Cedar Hill. I like keeping my CYA close to 60. I usually don't get too much over 2 ppm FC loss during the day, on a normal blazing day, with light swimmer load, and lower winds, blowing less than usual dust into the water, as it has been for the past week. A loss of 3 or more, during the day, in my pool, would be suspect.

I started with CYA around 60 at the beginning of July, didn't do any backwashing, but did have to let some water out a few times due to rain a few times and overfilling at least twice, some splashout (My evaporation can range from .5 to 1 inch per day depending on the wind. I brought CYA up to 60 a couple of days ago as it was getting somewhere between 40-50. Even at that lower point I wasn't getting much over 2 ppm loss during the day.

One 182 oz jug 6% bleach every other day pretty much keeps things fine and dandy; occasionally a tad more if conditions call for it. I usually get about half my bleach at Costco the other half Walmart brand. Usually get about a weeks worth at a time and store in big shaded steel shed or slightly cooled converted garage.

pH, hummmmmmmmm. I attempt to keep mine at 7.2, as I'm treating for calcium scale. I like to add MA daily but sometimes miss a day. It hasn't gotten over 7.5 in almost a year.

Right now with current sun's angle I'm getting about 7 full hours of sun on the pool a day.

gg=alice

EDIT--May be another factor. I run my pump 21/7, usually 19 gpm but the cleaner(s) running adds more turnover, and which ever cleaner I use runs several hours a day, usually split into 2-3 cleaning cycles per day. So my water is rarely still and the circulation all over the pool is very good; no dead spots. Bottom drain fully open unless using the vacuum cleaner.

 

[RoberTX]

gg

Thanks for the input. We have very similar situations as we are in the same place, with the same sized pool. I will be very happy if I can get by with only 1 jug of bleach every other day! It would be a nice change of pace from 3 jugs every day! I've been buying 2 carts full (12) twice a week at wal-mart!

It's also good to see that I'm not the only one with some level of CYA loss. Although mine seemed a bit higher than yours, and we got close to the same amount of rain (although there were a lot of cannonballs a few days...

I've got one knee-high in a skimmer basket and one in front of a return jet (4 lbs CYA total added). My FC is about 13 (from the bleach last night and the dichlor today).

Once the FC goes down, I'll check the pH and test the CYA again about 4 days after it's all dissolved.

I wish I knew before what I know now, I would have drained less water, targeted 60 instead of 50 CYA, and the light bulb :idea: would have gone off a lot sooner when the chlorine demand went up.

Oh well, lessons learned. I guess experience is what you get when things don't go perfect.


Robert

 

[geekgranny]

Robert, Wait longer before testing the CYA. It can take more than "a few days" for it to register on test. Just guesstimate what it should be and add bleach accordingly. I usually target FC for at or a little above my top number of range and don't worry if it is a little higher as it won't be nearly close to shock levels. That's FC 9 for a CYA of 60.

I didn't find TFP until last summer. We inherited this pool when we moved here 24 years ago. I've probably amassed more mistakes under my belt (interesting, my belt size has grown over the years, maybe it's all the pool mistakes, um yes, that's it) than a HUGE number of TFP members' mistakes all put together. I didn't start really learning from many of those many, many pool "mistakes" I made over the years, until I found TFP. Then the light bulbs started popping on so fast I was almost blinded. I did have the typical resistance, for a couple of weeks or so, to yanking out the Ionizer.

When people ask me how I've learned how to do so many things my answer is, "Don't be afraid, curiosity, research, learn from mistakes." It has been hard to learn from pool mistakes especially in years past, with so little understanding by even "experts".

I didn't have much curiosity to change my pool ways until last year as I was going along merrily ignorant using Ionization, for almost two decades, and never, ever having any algae (unless I shut the pool down in winter without really closing and no cover) and bragging about it any time I could get the chance; even converted a few people. Everything "blew up" last year especially when I realized that I could not acid wash my old plaster any more times along with the economy, and reduced income. Replaster would not be as viable an option as it had been in the past especially with old house needing more and more repairs.

I would put my experience with calcium scale, copper stains, iron stains, organic stains up against the "best" of them. I'd probably still be the Supreme Ruler. :queen: (as far as past experience)

Her Highness