huge clorine demand

[sabres07]

Since i openned my pool in early May, I have been expeiencing a huge chlorine demand. I thought my testing reagents might be old and giving me bad results so all have been replaced. i stll have chlorine demand of 6-10 ppm each day. Water is crystal clear. I have kept the pool above shock level for 9 days now and overnite i still lost 4 ppm. What could be my problem?? Here are my latest numbers- FC 26.5. Ph 7.6. Cc 0.0. tA 110. Stabilizer 50. My FC was well over 30 last nite at 11 pm.

[sabres07]

Added info: I re-tested and FC was down to 18.5 which means I lost 15 ppm in less than 24 hours with no swimmers usimg pool. Water is crystal clear and I have held pool over shock level for 9 days. I need help!

[JimK]

Added info: I re-tested and FC was down to 18.5 which means I lost 15 ppm in less than 24 hours with no swimmers usimg pool. Water is crystal clear and I have held pool over shock level for 9 days. I need help!

Did you lose CYA over the winter? As I understand it, CYA can be eaten by certain bacteria over the winter and the resulting byproducts (sorry, I forget exactly what they are) create a huge CL demand in the spring. I've experienced this several times, although for seem reason it did not happen this past winter. If this is the case you will just have to keep at it with CL until all the byproducts are gone.

Hopefully someone more knowledgeable will chime in as well.

[BigDave]

I don't claim to be more knowlegeable but, I would expect to see high CC, low FC and no (or severely depleted) CYA if sabres07's pool had experienced the CYA eating, ammonia excreting bacteria.

Perhaps it's bio-load, although I'd expect to see some CC.
Is there alot of pollen? Maybe there's lots of biological material in the filter being consumed by the chlorine not but reading elevated CC because the hich FC in the pool is doing away with the CC before it can be read. Just a Wild Antelope Guess. How's the filter?

[JimK]

I don't claim to be more knowlegeable but, I would expect to see high CC, low FC and no (or severely depleted) CYA if sabres07's pool had experienced the CYA eating, ammonia excreting bacteria.

Perhaps it's bio-load, although I'd expect to see some CC.
Is there alot of pollen? Maybe there's lots of biological material in the filter being consumed by the chlorine not but reading elevated CC because the hich FC in the pool is doing away with the CC before it can be read. Just a Wild Antelope Guess. How's the filter?

Ah, I missed that CC is measuring 0. Thanks for catching that. :)

[sabres07]

A few days ago, I thought maybe something was living in my filter cartridge, so I removed that and continued with my program of keeping the pool at shock level. Still no change. Also, I thought it might be the amonia issue due to degraded CYA because I had that problem last year. I have a 40-50 CYA reading this spring which is only down slightly from closing last fall. There was a lot of pollen a week ago, but has since not been an issue.

My plan is to continue with holding above shock, but this is getting ridiculous!! Like I said, the water is crystal clear and inviting. No visible signs of any issue other than my crazy chlorine readings....

[sabres07]

Ok....this is getting frustrating! My FC went from 35.5 last nite at 11 pm to 19.5 at 8 pm tonite. This is getting expensive. There must be a problem that i cant figure out. I am about to recover this pool and call it a day!

[chem geek]

Since you said you checked your filter, I assume you checked other places such as your skimmer and pump basket. You might also check under any removable ladders and perhaps behind light niches. Something is seriously consuming chlorine in your pool, and losing it overnight means it's not the UV in sunlight.

I also assume you test your chlorine level within an hour after you've added it just to make sure your chlorine isn't weaker than you think. So I too am at a loss. This is very unusual. Even if it were some conversion of CYA to ammonia and/or partially oxidized CYA, you should see your chlorine demand dropping and you would see at least some CC.

[sabres07]

Since you said you checked your filter, I assume you checked other places such as your skimmer and pump basket. You might also check under any removable ladders and perhaps behind light niches. Something is seriously consuming chlorine in your pool, and losing it overnight means it's not the UV in sunlight.

I also assume you test your chlorine level within an hour after you've added it just to make sure your chlorine isn't weaker than you think. So I too am at a loss. This is very unusual. Even if it were some conversion of CYA to ammonia and/or partially oxidized CYA, you should see your chlorine demand dropping and you would see at least some CC.

Yes, I do check chlorine levels after adding. For example, last night at 9 PM I added 8 gallons of 6% bleach and raised my FC level from 19.5 ppm to 42-43 ppm which it tested at 11 PM. This morning at 7 AM, my FC level was 37 ppm, for a loss of 4-5 overnight. I had a similar loss the night before of 5-6 ppm. No cc reading this morning, either. I will check behind my light housing today. Pump basket is clean. Under ladder looks clean, too.

I am at a loss here and it is getting very expensiive!!

The reason I took it up to high 30's for FC is that keeping it at the shock level recommended by the BBB method wasn't working. The chart recommends 20 ppm for shock level for me.

[BigDave]

Is it at all possible that you're testing CC and FC out of order? I'm sorry for asking, but I've been puzzling over this issue. The FAS-DPD test method is:
Measure pool water sample(I'm presuming 10ml)
Add a scoop or two of R-0870 DPD powder and swirl until solution turns pink.
Add the R-0871 titrating solution counting each drop and mixing.
Multiply drop count by 0.5ppm to get FC reading.
Add 5 drops of the R-0003 DPD Reagent #3.
If the solution turns pink again:
Add R-0871 solution counting each drop and mixing.
Multiply drop count by 0.5ppm to get CC reading.

I hope you're not offended, this is a real headscratcher.

[sabres07]

Is it at all possible that you're testing CC and FC out of order? I'm sorry for asking, but I've been puzzling over this issue. The FAS-DPD test method is:
Measure pool water sample(I'm presuming 10ml)
Add a scoop or two of R-0870 DPD powder and swirl until solution turns pink.
Add the R-0871 titrating solution counting each drop and mixing.
Multiply drop count by 0.5ppm to get FC reading.
Add 5 drops of the R-0003 DPD Reagent #3.
If the solution turns pink again:
Add R-0871 solution counting each drop and mixing.
Multiply drop count by 0.5ppm to get CC reading.

I hope you're not offended, this is a real headscratcher.

Ha...not offended at all. In fact my son asked me the same thing. I am testing properly I believe.

I just tested again at 10 AM. My FC is now down to 28-29 ppm (last nite at 11 PM it was 43!). I didnt believe those results so I tested it a second time and got the same number. Also, I did get a slight reading on cc this time, too, of 0.5<. Also, the water is crystal clear.

I am starting to think that draining the pool down by half and re-filling might be a cheaper way to go.

Any thoughts??

[BigDave]

Maybe try a Chlorine Demand Bucket Test (http://www.poolforum.com/pf2/showthread.php?16973-Bucket-testing-for-chlorine-demand) to help figure out what's going to help. I'd start tonight and do an overnight test of just plain pool water to see if it's something in the water or something else causing such high chlorine consumption. After tomorrow morning, start dosing the bucket to see what it will take to get chlorine to hold - if you can at all. Then figure out if the chlorine or the water will be cheaper. Also maybe also do a bucket test with half pool water and half fill water to see if that's going to help.

[sabres07]

UPDATE: Last nite was the first nite my FC held from sundown to sunrise. I pulled my light niche and found a whole lot of crud back there. Very disgusting. So I scrubbed it all out and left the light out for two days so that shocked pool water could circulate in there. Maybe that was the problem with my huge chlorine losses. To re-cap, I had my pool at shock level (above 20 ppm) for at least 12-13 days now. It took that long to defeat whatever was in my pool. Hopefully I am done now. I will keep it up above shoock for at least one more day to be sure.

[JimK]

UPDATE: Last nite was the first nite my FC held from sundown to sunrise. I pulled my light niche and found a whole lot of crud back there. Very disgusting. So I scrubbed it all out and left the light out for two days so that shocked pool water could circulate in there. Maybe that was the problem with my huge chlorine losses. To re-cap, I had my pool at shock level (above 20 ppm) for at least 12-13 days now. It took that long to defeat whatever was in my pool. Hopefully I am done now. I will keep it up above shoock for at least one more day to be sure.

Good to hear! Thanks for the update.