Chlorine consumption seems to be double this year. Why?

[joninnj]

Hello! This site saved my bacon as a new pool owner last year. Pool and water were great last year, settling into using a little less than one gallon of bleach/day (I could skip a day every week or so). However, this year, it seems to be consuming two gallons of the same bleach a day. Double!

At the risk of providing too much information, here is everything that may be relevant.

Basic pool stats:
20x40 vinyl liner pool in NJ, guessing 30,000 gallons or a little less, DE filter, NEW PUMP replaced broken pump this spring (same pump as the old one, which was very old: Pentair WhisperFlo 2 HP).

Closing: I had a new company close the pool last fall and open it again in the spring. At close, they just used the Polyquat and bleach I left them. Mesh cover.
Opening: Pool not opened until June. They added liquid chlorine, calcium, and "alkalite." Besides the new pump, the only thing that seemed "off" is that there was a sweet smell around the pool for a few weeks. The water itself, when smelled up close, didn't smell sweet, but the air around the pool did. Clear water with passed OCLT less than a week after opening.

Bleach: I use Walmart 8.25% bleach or the Walmart liquid pool chlorinator (10% bleach). I always try to get the freshest stuff, and the liquid chlorinator I got at the beginning of the season was on the "old" side, but I am now using fresher bleach and still having the same issue of seemingly double chlorine consumption.

Pool testing: I have always used the TF-100 test kit. I got a whole new set of reagents this year and tossed the old ones. As for chlorine readings, when FC is low enough, the Taylor test results seem to corroborate the drop test results.

Final results from last year before close (and consistent with what I had all summer):
pH 7.5 FC 12 CC 0 TA 80 CH 175 CYA 60

Results from this summer:
After opening before OCLT: pH 7.5 FC 6 CC 0 TA 130 CH 260 CYA 50
After OCLT: pH 7.5 FC 8 CC 0.5 TA 120 CH 175 CYA 50

Water has been good and clear all season. pH has always been rock solid (last year and this year). CC has never been higher than 0.5. I did a small drain after some heavy rains, but the CYA was unchanged afterward (50).

So why is my pool "consuming" double the chlorine this year? I don't think it's the bleach or testing reagents, but could those be the problem? Could this be a result of a slightly lower CYA (60 to 50)? More efficient pump? Anything? Again, the water is great. My main concerns are 1) there's something "consuming" the chorine that I am missing, and 2) I am tired of lugging double the number of bleach jugs .

Thanks for any thoughts on my little problem!

 

[Richard320]

How long have you been open?

If they blew the antifreeze into the pool when they opened, that could easily account for the sweet smell and the extreme chlorine demand. Antifreeze and Chlorine

 

[joninnj]

How long have you been open?

If they blew the antifreeze into the pool when they opened, that could easily account for the sweet smell and the extreme chlorine demand. Antifreeze and Chlorine

I had thought of that. But its been almost 4 weeks since open (June 6), and the sweet smell is gone, but still consuming 2 gallons/day. I was waiting for that plus fresher chlorine before posting...

 

[joninnj]

How long have you been open?

If they blew the antifreeze into the pool when they opened, that could easily account for the sweet smell and the extreme chlorine demand. Antifreeze and Chlorine

If this is an antifreeze effect, how long might I expect to last?

 

[Richard320]

If this is an antifreeze effect, how long might I expect to last?

I have no clue. I just remembered reading that.

 

[joninnj]

Just read through the Walmart bleach/chlorinator thread. I am hoping this is just weak bleach/chlorine and the anti-freeze issue and will resolve in the next few weeks. I really don't want to have to dump in 2 gallons of bleach a day! Any other thoughts?

 

[pookiesunshine]

test tonight about 30 min after adding bleach to see if your target was achieved. if not, maybe weak bleach.

 

[joninnj]

Bleach seems to be good. I may do another OCLT just to be 100% sure there is no residual algae (though the completely clear pool with CC readings of 0 or 0.5 make me think this is unlikely).

I am wondering if there is any possibility that the higher chlorine consumption could be pump/filter related:
1. Worth backwashing and re-adding DE? Pressure has been stable. As I mentioned up top, pool was opened by a new company. Might they have messed up something with the DE?
2. Could this be related to water flow? New company converted the old (closed) pressure port to a jet. Might that negatively affect circulation and lead to decreased filtering and increased chlorine consumption?

 

[Richard320]

Bleach seems to be good. I may do another OCLT just to be 100% sure there is no residual algae (though the completely clear pool with CC readings of 0 or 0.5 make me think this is unlikely).

I am wondering if there is any possibility that the higher chlorine consumption could be pump/filter related:
1. Worth backwashing and re-adding DE? Pressure has been stable. As I mentioned up top, pool was opened by a new company. Might they have messed up something with the DE?
2. Could this be related to water flow? New company converted the old (closed) pressure port to a jet. Might that negatively affect circulation and lead to decreased filtering and increased chlorine consumption?

You've been talking to the pool store people, haven't you? They always blame the filter when they mess up the chemistry.

Unless you have dead critters decomposing in the filter -- and I don't see how they would have gotten past the baskets -- there's nothing in the filter that can use that much chlorine on a daily basis. DE is mostly silicon and the rest is plastic.

As for circulation, poor circulation could lead to algae growth in the dead spots which would lead to increased chlorine demand. Regular brushing should counter the poor circulation by moving chlorinated water into those areas.

It's either algae or residual antifreeze.

 

[joninnj]

Nah, I have never spoken to pool store people about my water . Just grasping for straws.

For the filter, I was wondering if it is not working well enough, e.g. not enough DE in it or not enough water circulating through it. Even though the pressure has been stable, no harm in backwashing it ad re-adding DE anyway, right? It's almost been a month since opening. As for general pool cleaning, I do run my Nautilus weekly or so.

My current plan: OCLT and then backwash. I wish I could quantify the antifreeze effect and know how long it was going to hang around...

 

[Catanzaro]

Final results from last year before close (and consistent with what I had all summer): pH 7.5 FC 12 CC 0 TA 80 CH 175 CYA 60

Results from this summer: After opening before OCLT: pH 7.5 FC 6 CC 0 TA 130 CH 260 CYA 50

After OCLT: pH 7.5 FC 8 CC 0.5 TA 120 CH 175 CYA 50

A few questions:

1) If you look at your results from closing to opening, the figures changed. Did you add water from the township or other source, or did the water over the winter from snow and rain? Your CH figures bounced around a lot from closing to opening, etc. Also, your TA went straight up. Even a small amount of fill water should not have this effect unless you added chemicals. My CH and TA dropped because of the rain water and snow through the winter, and CYA as well.

2) You state that at closing they added poly-quat and bleach? Where did the antifreeze come from? Or am I missing something?

3) At what times did you add the bleach last year and when are you adding the bleach this year?

4) The bleach that you are using that is twice as much? Is it old bleach from last year?

Something does not add up. The filter is not the culprit. Regarding pool company, opening and closing, the only thing they should be doing is that and not adding any chemicals. It appears that you understand chemistry, so no need for pool company chemicals. Ever thought of closing your own pool? Opening is a breeze.

 

[pookiesunshine]

.... New company converted the old (closed) pressure port to a jet. ...

Was this just a leg off the main line or a longer line? maybe some mold or such built up in it while closed off. no flow means stagnant. if it has a biofilm build up, chlorine levels in pool water may not be enough to clear it up. maybe a bottle brush or similar you can stick in there to see if there is any build up in this recently opened line. just a thought.

 

[joninnj]

Appreciate the thought and questions. Replies below:

A few questions:

1) If you look at your results from closing to opening, the figures changed. Did you add water from the township or other source, or did the water over the winter from snow and rain? Your CH figures bounced around a lot from closing to opening, etc. Also, your TA went straight up. Even a small amount of fill water should not have this effect unless you added chemicals. My CH and TA dropped because of the rain water and snow through the winter, and CYA as well.

Pool was drained to below skimmers at close. With the mesh cover, it definitely accumulated water over the winter. Not sure if at open it had to be topped of, drained off a bit, or if it was at the right level. Guessing TA went up from the "alkalite" they added at opening.

2) You state that at closing they added poly-quat and bleach? Where did the antifreeze come from? Or am I missing something?

Yes, they did add antifreeze of their own at closing last fall. I did not provide it/specify which antifreeze because it didn't seem to be critical (unlike the poly-quat vs. other algaecides) from what I have read here.

3) At what times did you add the bleach last year and when are you adding the bleach this year?

Always in the evening with the sun set or mostly set. That hasn't changed.

4) The bleach that you are using that is twice as much? Is it old bleach from last year?

Nope. All new bleach from the same source (Walmart).

Something does not add up. The filter is not the culprit. Regarding pool company, opening and closing, the only thing they should be doing is that and not adding any chemicals. It appears that you understand chemistry, so no need for pool company chemicals. Ever thought of closing your own pool? Opening is a breeze.

If this is not the filter, could this all be the antifreeze?

- - - Updated - - -

Was this just a leg off the main line or a longer line? maybe some mold or such built up in it while closed off. no flow means stagnant. if it has a biofilm build up, chlorine levels in pool water may not be enough to clear it up. maybe a bottle brush or similar you can stick in there to see if there is any build up in this recently opened line. just a thought.

I used this line for the first month last year while I was trying to get the pressure robot to work, so it's not that dormant. I will try another OLCT this weekend, though, to try to rule out consumption.

 

[Catanzaro]

Everything sure leads to the anti-freeze. IMO, it appears the pool company is safeguarding against their work. Eventually, the consumption will stop. Maybe calling the manufacturer to determine its properties may be a good idea. Outside this, have you ever thought about closing your own pool?

I do not use antifreeze at all. The last few years, I have experimented with 3" 4 foot round tube filled with 90% water. Glued the bottom and left the top just capped. The cap did not move from the black mark. The second year, the water was filled up 99% of the way up. The cap actually moved up about 1" (if you can follow this) due to ice expansion. Nothing cracked.

Most of the piping, especially the main drain is too far underground for freezing. Where I feel most of the damage could be is due to high water tables, freezing water in soil and movement that could damage the underground plumbing. Essentially, antifreeze is an extra expense passed on to the homeowner. The first year closing of $275 did the trick for me. That was the first and last time I used a pool company.

If you want to tackle your own closing this year, I can help. If not, please have them not put any chemicals in at closing. Hire them only to blow out the system. You can see what frustration it can cause.

 

[joninnj]

Yes, thanks for the advice. Will seriously consider this for the fall. Glad to hear people don't think it's the DE filter or pool flow. Consumption SEEMS to be slowing down a bit. We'll see over the next few days.

 

[joninnj]

Doing a SLAM/OCLT tonight to take that off the table.

Question: if none of you think the filter could be an issue here, how does one assess how well the filter is working? Is it simply water clarity and nothing to do with chlorine consumption?

 

[pooldv]

That is correct. The filters only job is to remove particulates from the water. Everything else is based on water chemistry. Two things typically consume more than expected chlorine, bacteria and algae. Unless it is a one time drop then it is usually some bird or varmint poo. The way to solve that is more chlorine to kill what is consuming the chlorine.

 

[joninnj]

Is my FAS/DPD test off?

I completed another OCLT today. I THINK I passed. The reason I am not sure is that I got very different FC readings. The post-SLAM evening FC was 19.5. This morning at sunrise, the FC reading was 24! The water might have been slightly high, no more than 11 cc. So I repeated it. This time, 16! The water might have been slightly low but more than 9 cc for sure. So I repeated it a third time, being very careful on the water level: exactly 19.5! Any idea why I am getting such wildly fluctuating levels? Since I started doing this last year, I have always had what I thought were rock solid FC readings. I use the magnetic stirrer. I have never been that careful with the water levels, power, and drops because it didn't seem to matter that much. However, this summer, maybe related to my uncertainties on bleach consumption, the readings sometimes seemed a little different than expected. Could my reagents, newly purchased this summer, be off? I also purchase a new mixing tube and little blue spoon. I do not think this is the "cause" of my bleach consumption issue, but who knows? I may buy more FAS/DPD reagents just to be sure.

The other thing I am wondering about: CH has dropped from 260 to 175 to 125. Any idea what is going on here? Related ti bleach consumption? User testing error? Last summer, it slowly drifted down from 300 to 175, and the new pool company added calcium at opening this year.

 

[Akathisia]

Check out the Sample Sizer if you want to speed up your testing and increase precision. You also need to use Taylor Calibrated Cylinders with the Sample Sizer.

TFTestkits.net
TFTestkits.net

 

[poolnewbies5874]

What about a cover? Did you have a solar cover on your pool or anything last year? If we keep our solar cover on we don't consume as much chlorine but if we leave it off we use almost double...