monster that eats chlorine in my pool

in-two

Well-known member
Nov 13, 2011
51
Sabina, Italy
In three days I have used 900 litres (237 gallons) 15-17% bleach, 60 kgs 132 lbs) Dichlor, and 60 liters (15 gallons) of muriatic acid! My pool is still green/yellow, bottom barely visible, a lot of sediment.
Numbers this evening: FCL > 1, TCL 6, Ph 8.1, TA 9, CH 2 , CYA 28 .
No, these are not misprints... although the single figure TA and CH may be out of range readings from my color Q. Reagents are fresh.

Pool is less than half full, about 20,000 galls.

History: Had to drain pool for the first time in 9 years to carry out essential plumbing repairs, changing out rusted galvanized steel pad piping, manifolds, valves etc which were beyond repair and leaking seriously, for all PVC. Pad is below the pool waterline. This went well with one exception, and is now all working and watertight, pump is good, filter also.
I take my water from a local creek that is pumped up from the valley bottom to a large, concrete, closed holding tank, then pumped into the pool. Tank holds about 1/3 pool volume and also collects rainwater runoff from roofs and driveways.
The exception is that I forgot to solvent weld one joint, one of the lowest ones, of course ... duh! Started to fill, noticed the leak, pumped the water back into the holding tank, fixed leak, started to fill again. Water very quickly went green and threw a yellowish sediment despite me 'firebombing' it with chlorine as the fill started. Very likely the pump back process stirred up sediment etc. in the holding tank. I have no other source of water. I stopped the fill at half way (main drain and returns all under water and pumping) then went SLAM crazy as the above quantities show, managed to get the Ph down to 7.0 briefly, but absolutely no significant FCL showing at hourly testing and essentially adding bleach, then dichlor as fast as I could throw it in.
I have managed the pool for several years with no significant issues thanks largely to what I have learnt here on TFP (big thanks) with the same water source and testing regime and am reasonably familiar with both the chemistry and the hydraulics of my pool, but this really has me stumped. I can only imagine that there is some kind of algal growth that is consuming impossible amounts of chlorine. Please make any suggestions of what I can do next. I'm on the verge of giving up, trying to source a tanker supply of water (difficult, really expensive, 10 loads or more, 160 tonnes of water... ) Naturally my daughter is turning up at the weekend with 20 friends for a pool party, oh well.
 

domct203

Bronze Supporter
LifeTime Supporter
TFP Guide
Jun 3, 2015
3,959
CT
In three days I have used 900 litres (237 gallons) 15-17% bleach, 60 kgs 132 lbs) Dichlor, and 60 liters (15 gallons) of muriatic acid! My pool is still green/yellow, bottom barely visible, a lot of sediment.
Numbers this evening: FCL > 1, TCL 6, Ph 8.1, TA 9, CH 2 , CYA 28 .
No, these are not misprints... although the single figure TA and CH may be out of range readings from my color Q. Reagents are fresh.

Pool is less than half full, about 20,000 galls.

History: Had to drain pool for the first time in 9 years to carry out essential plumbing repairs, changing out rusted galvanized steel pad piping, manifolds, valves etc which were beyond repair and leaking seriously, for all PVC. Pad is below the pool waterline. This went well with one exception, and is now all working and watertight, pump is good, filter also.
I take my water from a local creek that is pumped up from the valley bottom to a large, concrete, closed holding tank, then pumped into the pool. Tank holds about 1/3 pool volume and also collects rainwater runoff from roofs and driveways.
The exception is that I forgot to solvent weld one joint, one of the lowest ones, of course ... duh! Started to fill, noticed the leak, pumped the water back into the holding tank, fixed leak, started to fill again. Water very quickly went green and threw a yellowish sediment despite me 'firebombing' it with chlorine as the fill started. Very likely the pump back process stirred up sediment etc. in the holding tank. I have no other source of water. I stopped the fill at half way (main drain and returns all under water and pumping) then went SLAM crazy as the above quantities show, managed to get the Ph down to 7.0 briefly, but absolutely no significant FCL showing at hourly testing and essentially adding bleach, then dichlor as fast as I could throw it in.
I have managed the pool for several years with no significant issues thanks largely to what I have learnt here on TFP (big thanks) with the same water source and testing regime and am reasonably familiar with both the chemistry and the hydraulics of my pool, but this really has me stumped. I can only imagine that there is some kind of algal growth that is consuming impossible amounts of chlorine. Please make any suggestions of what I can do next. I'm on the verge of giving up, trying to source a tanker supply of water (difficult, really expensive, 10 loads or more, 160 tonnes of water... ) Naturally my daughter is turning up at the weekend with 20 friends for a pool party, oh well.
Are you 100% certain on those chemical additions?

Are you not familiar with the SLAM Process process? Do you normally follow the [FC/CYA][/FC/CYA]?

Do you understand what else comes along with dichlor in addition to chlorine?

132 lbs of Dichlor would raise FC by 209ppm, and add 190ppm to CYA. With a CYA of 190ppm, you would need to maintain a FC of 76ppm to completely kill any algae and make the pool sanitary, which is unrealistic and would be very expensive to attempt.

If you did indeed add 132 pounds of Dichlor, I'm afraid that your only option is to drain about 3/4 of the pool and refill to get your CYA back down to a manageable level.
 

in-two

Well-known member
Nov 13, 2011
51
Sabina, Italy
Thanks for your reply, and interest.
It is exactly because the pool is not reacting in the expected way that I posted. During the whole process I monitored FC, TCL and CYA carefully for exactly the reasons you mentioned. I have used the FC/CYA chart for years and have SLAMed successfully in the past.
I only started adding dichlor after putting in huge quantities of liquid bleach as my CYA levels were very low, less than 20, the water was 'new'. CYA crept up to 28 ppm after all the dichlor, FC has never exceeded 1 ppm, quantities are correct, I have all the empty containers. I suspected dramatic testing errors and quadruple checked everything, pool water reacts as if there is no FC and very high TCL and this was happening before adding the dichlor, which I don't usually use. It was added as a 'last resort', thinking that bright sunlight and algae were consuming chlorine faster than I could add it.
I may have had a dramatic under reading of the CYA level due to instrument failure, but the FC levels are unequivocal, the DPD 1 tablet just fizzes and the solution remains clear, no pink at all and that was before the dichlor addition.
I would completely admit that I may have this all wrong, but am searching for either my error, or the cause.
I am now more or less committed to a complete drain and re-fill from trucked in water. I'll let you know how it goes.
 

Skimis

Member
May 9, 2017
18
Galloway, NJ
Just a couple of thoughts. Sand filter on 42,000 gal will take quite a while to clean out anything you do manage to kill - I'd make sure it's not contaminated. I had a similar problem a year ago... dumped 50 gallons of liquid chlorine in a 21,000 gal pool and couldn't get a FC reading. Turns out I had a significant amount of ammonia as a result of a high CYA combining with bacteria/organic material over time. And ammonia eats chlorine like crazy. I found this after someone in the forums suggested I test for it. Draining down your pool sounds like the best bet - good luck!
 

domct203

Bronze Supporter
LifeTime Supporter
TFP Guide
Jun 3, 2015
3,959
CT
If you are 100% certain on the Dichlor addition I would say you have some serious testing error on the CYA result. What is the upper limit to your CYA test?
 

in-two

Well-known member
Nov 13, 2011
51
Sabina, Italy
Thanks for joining in, Ski,mis, ammonia may well be an issue, my water supply is a creek in a farming area so ammonia based fertilisers may well be in the run-off. Don't yet know how to test for that but will find out.
As for CYA, I have no reason to believe there was any in the fill water initially but fully understand that I added a huge quantity with the dichlor, and , despite tests continuously showing less than 30ppm, it must be in there somewhere and not showing up on testing. My Color Q 7 photometer has previously been reliable and consistent, don't know the upper reading limit for CYA but will find out. Am wondering if the very high Ph readings (above 8,4) might also affect CYA accuracy, please advise if anybody knows. Thanks for your continued interest, domct.
pool emptied today, water trucks arriving tomorrow.
 

zea3

Mod Squad
TFP Expert
LifeTime Supporter
Jul 10, 2009
12,694
Houston, Texas
Any store that sells pet/aquarium supplies should have an ammonia test kit. The test is pretty easy and you can read the result in 5 minutes. If you do have ammonia, the answer is liquid chlorine in very quick additions. Add enough to reach 10ppm, keep the pump running and retest in 30 minutes. If you lose more than 1/2 the FC raise it back to 10ppm and retest in 30 minutes. Keep that cycle going until the chlorine starts to hold, then test and dose every hour. Do not use any CYA until all the ammonia is gone.
 

in-two

Well-known member
Nov 13, 2011
51
Sabina, Italy
I think I have just found out what has been going on, I am trucking in water and chlorinating as I go, over enthusiastically as it turns out. I have superchlorinated and its bleaching out the DPD test. What threw me last time was the green/yellow cast to the water, which I now believe to be sediment from the previously described creek water. I just threw in more chlorine, thinking something was consuming it.
This time I put in a bit more chlorine than recommended overnight, then some more this morning. On testing got a very low reading <1. On dilution of the same sample I got back to a high reading >10ppm on FCL. Checked out 'bleaching of DPD' and found exactly my symtoms. Good part of this is that I have now managed to properly dis-infect the filter and all is running clear. I will now run diluted samples until additional truck loads of water bring me back to correct levels.
Thanks for your interest and suggestions, I don't have any pet stores nearby but will find one and see if ammonia is a factor in my creek water.
My real problem seems to have been over-enthusiastic SLAMing and the limitations of my testing regime. An expensive lesson learned.
 

domct203

Bronze Supporter
LifeTime Supporter
TFP Guide
Jun 3, 2015
3,959
CT
I think I have just found out what has been going on, I am trucking in water and chlorinating as I go, over enthusiastically as it turns out. I have superchlorinated and its bleaching out the DPD test. What threw me last time was the green/yellow cast to the water, which I now believe to be sediment from the previously described creek water. I just threw in more chlorine, thinking something was consuming it.
This time I put in a bit more chlorine than recommended overnight, then some more this morning. On testing got a very low reading <1. On dilution of the same sample I got back to a high reading >10ppm on FCL. Checked out 'bleaching of DPD' and found exactly my symtoms. Good part of this is that I have now managed to properly dis-infect the filter and all is running clear. I will now run diluted samples until additional truck loads of water bring me back to correct levels.
Thanks for your interest and suggestions, I don't have any pet stores nearby but will find one and see if ammonia is a factor in my creek water.
My real problem seems to have been over-enthusiastic SLAMing and the limitations of my testing regime. An expensive lesson learned.
This is another reason we do not recommend a DPD test. The FAS/DPD will read FC up to 50ppm, without ‘bleaching out’.

And technically, you were not SLAMming, as your current test kit limits your ability to do that properly.
 

in-two

Well-known member
Nov 13, 2011
51
Sabina, Italy
Sorry about the delay in replying, been swimming in my crystal clear pool and clearing up after my daughter's pool party, she left behind a few cases of beer, so no hardship.
So, twenty bowsers of clean clear spring water and careful dosing with bleach and a bit of dichlor to get some CYA and it's all good. Understand the limitations of the DPD test and find it a PITA although careful dilution of the test sample yields acceptable results.
As for Sabina, it's history as the idyllic holiday playground of Roman emperors is well deserved, we love it. So Seadweller, come on over, we have several neighbours who have escaped from The States and have no intention of returning. Some friends from England turned up, stayed a couple of days by our pool and went and bought a house nearby, took less than a week, and if you saw the view of the Soratte mountains from their terrace, you would understand why.
Back to the pool; whilst it was drained I discovered that the floor is not cement as I thought but a layer of glass fibre over concrete which I needed to patch in a few places after vigorous jet washing had exposed a few holes. It had also been painted a couple of times in it's 40 year life judging by the flakes that came up. I will contemplate re-finishing it over the next few years and will be seeking advice, probably in the 'under construction' section. Thanks again for everybody's interest.