Chlorine level starts dropping

[tempus]

CYA 70
FC 5
CC 0
PH 7.4
TA 80
CH 210
Salt 4420

My problem is that I can maintain pool chemistry for a couple of months, but then my FC level will start to drop and I can't recover with the SWG.

The pool chemistry got messed up by Irma. We were without power for 8 days. I added bleach daily to try to maintain FC but with no circulation and filtering I had to SLAM the pool once power came on, as there was just a touch of algae (very slight cloudiness to the water). It has been good since then, until now. I test FC and PH daily, the rest weekly or so. CYA maybe every 3 weeks. The problem is my FC will start to drop from 5-7 where I try to keep it. This time of year the pool is not used and has a thermal cover. I run the pump 3 hours per day. The SWG was set at 3/8 which maintained FC for 6-7 weeks. Then the FC started to drop. I increase the SWG by one, then two, then full on, then add another hour to pump run time. The FC just keeps dropping, until it is down to 1-2 in the morning. By this time I had also used the "super chlor" button on the SWG, but I find I must add bleach to get back to FC of 5, which I did two days ago. This morning it has held at 5 from the same reading last night, and I have not added bleach. So I may be back on track.

This has happened 2-3 times before (I've had the pool two seasons now) and in the past I shut off the SWG and did a SLAM to get things back to normal.

I'm not sure if I'm being too lax in maintaining chemistry or what. I have allowed CYA to get as low as 50, and that is where it was this time when the FC started to drop. Do I need to be more diligent in this? Keep CYA higher?

 

[domct203]

CYA 70
FC 5
CC 0
PH 7.4
TA 80
CH 210
Salt 4420

My problem is that I can maintain pool chemistry for a couple of months, but then my FC level will start to drop and I can't recover with the SWG.

The pool chemistry got messed up by Irma. We were without power for 8 days. I added bleach daily to try to maintain FC but with no circulation and filtering I had to SLAM the pool once power came on, as there was just a touch of algae (very slight cloudiness to the water). It has been good since then, until now. I test FC and PH daily, the rest weekly or so. CYA maybe every 3 weeks. The problem is my FC will start to drop from 5-7 where I try to keep it. This time of year the pool is not used and has a thermal cover. I run the pump 3 hours per day. The SWG was set at 3/8 which maintained FC for 6-7 weeks. Then the FC started to drop. I increase the SWG by one, then two, then full on, then add another hour to pump run time. The FC just keeps dropping, until it is down to 1-2 in the morning. By this time I had also used the "super chlor" button on the SWG, but I find I must add bleach to get back to FC of 5, which I did two days ago. This morning it has held at 5 from the same reading last night, and I have not added bleach. So I may be back on track.

This has happened 2-3 times before (I've had the pool two seasons now) and in the past I shut off the SWG and did a SLAM to get things back to normal.

I'm not sure if I'm being too lax in maintaining chemistry or what. I have allowed CYA to get as low as 50, and that is where it was this time when the FC started to drop. Do I need to be more diligent in this? Keep CYA higher?

Can the pool pass an Overnight Chlorine Loss Test? If not, that would indicate algae and/or bacteria is alive and reproducing faster than your current FC level can kill it, and it's SLAM time. If the pool passes an OCLT, then the next probable suspect would be UV exposure (sun 'burning off' FC).

I would put my money on not being able to pass the OCLT and you have algae. With the thermal cover, and lower angle of the sun, the UV exposure is minimal. If you think you have slacked off on maintaining the proper FC level, chances are that you have.

 

[tempus]

It did just pass an overnight test dropping to 4.5 ppm from 5.5. My question isn't so much how to detect and treat as it is how to prevent.

 

[AftonJeeper]

My question ... is how to prevent.

To prevent algae growth you need to maintain a minimum FC for your CYA. If your FC falls to 1 or 2 as you stated it is too low. [FC/CYA][/FC/CYA]

If your water gets close to or below 60° during the winter your SWG will not work and you will have to supplement with bleach. Since your CYA is lower than the recommended level for a SWG pool you could use triclor to raise CYA and to maintain a proper FC level.

During the winter months it is okay to run a lower CYA because the sun isn't as powerful so you could put off raising the CYA until spring.

 

[tempus]

Thanks. CYA is currently 70 which should be OK, no? Yes, it did drop to 50 - sounds like that may be the source of my problem? This is what I am trying to figure out.

I understand that FC 1-2 is too low. The problem is that my target is higher in the 5 to 7 range, and I can maintain that for weeks with only 3 hours of pump run time (winter) and SWG at 3/8, then FC unexpectedly starts dropping and I can't keep it from falling by increasing SWG and pump run time alone. It seems that I should be able to find an maintain a balance. If I run the SWG at 8/8 for a period of time the FC climbs up to 10 and beyond. I'm trying to find and maintain correct balance. Am I having trouble because I'm not maintaing CYA at 70-80? Is my FC target too low?

 

[mknauss]

A CYA of 70 is fine. As you stated in the past your pool is covered - so not much sunlight getting to the water.

How often do you take the cover off? You need to let the water breathe every few days as long as the water is above 60F. That will burn off the CC's that build up.

Is the scenario of weeks of consistent FC followed by a sudden drop also have the cover on the pool all the time?

Good luck.

 

[ping]

Was the pool running overnight when you did the OCLT and was the SWG turned off? If either of these answers are no, repeat the OCLT with the pump running and the SWG turned off. Losing 1ppm overnight at this time of year is substantial with only starting off at 5ppm of FC.

My guess is the pool needs to go through a complete SLAM along with the cover.

Make sure the SWG is clean of scale, don't clean it with acid if it doesn't have scale.

 

[domct203]

It did just pass an overnight test dropping to 4.5 ppm from 5.5. My question isn't so much how to detect and treat as it is how to prevent.

There are only two major 'consumers' of FC.... Organics (algae, bacteria, bather waste, etc) and UV (sunlight). If the pool can pass an OCLT, that rules out organics. We cant help you prevent what is happening if we do not understand what is happening in the first place.

As mentioned, is the SWG off when performing the OCLT?

 

[tempus]

How often do you take the cover off? You need to let the water breathe every few days as long as the water is above 60F. That will burn off the CC's that build up.

I have not been taking the cover off; I did not realize it was necessary. Thanks. The water is 73 now never gets below 68 here.

- - - Updated - - -

Was the pool running overnight when you did the OCLT and was the SWG turned off?

The pump was not running overnight. I do not see that in the OCLT instructions. I was not aware it should be on.

- - - Updated - - -

As mentioned, is the SWG off when performing the OCLT?

Pump was not running so yes SWG was off.

 

[duraleigh]

My problem is that I can maintain pool chemistry for a couple of months, but then my FC level will start to drop and I can't recover with the SWG.

SWG's are good for maintaining a certain level but are often not powerful enough to make up too much loss or certainly to SLAM.

Use bleach to make up a loss.....not your SWG.

 

[domct203]

I have not been taking the cover off; I did not realize it was necessary. Thanks. The water is 73 now never gets below 68 here.

- - - Updated - - -

The pump was not running overnight. I do not see that in the OCLT instructions. I was not aware it should be on.

- - - Updated - - -

Pump was not running so yes SWG was off.

I recommend you do another OCLT, with the pump running and the SWG off. Be sure to have your FC in your target range per your CYA for the OCLT.

 

[tempus]

Picking up where this thread left off, I did SLAM the pool to target FC 28 ppm per the table. I was able to maintain that with no additional chlorine after a few days. With the SWG off FC dropped to 14 ppm by Dec. 20. As we were leaving for the holidays, not wanting to come back to a problem, I started the SWG at a moderate level. I expected that the FC might increase, and it did - when I returned Jan 4 it was 24 ppm. I turned the SWG off. Jan 20 FC was down to 18. When FC got down to 10, I started the SWG at 2/8 (pump running 3 hours). After a few days FC was down to 7, so I increased the SWG to 4/8. A few days later it was down to 5, so I went to 8/8 on the SWG. Yesterday FC was 4.5. I ran an overnight test and FC went from 4.5 in the evening to 3 this morning.

(All other chemicals were monitored during this time and not unexpectedly some fluctuated a bit - for example pH varied between 7.4 and 7.8 - but stayed within recommended range.)

OK, I know I need to SLAM the pool again. That is not the issue. The issue is, why am I getting into this situation in the first place?

 

[mknauss]

The last you reported your CYA was 70. Following the [FC/CYA][/FC/CYA], you came very close to the minimum FC. Also, are you testing your water at the same time each day? Preferably right before your SWCG starts for the day? That is the lowest the FC will be in your water each day. That ensures you are managing your SWCG run time based on the lowest FC your pool sees each day.

Check the skimmer, skimmer weir, any lights, any other areas that algae might hide.

Do you get ducks, birds, other critters that deposit organic material in your pool?

Good luck.