Chlorine Problem ? Help

[jwm9289]

i have a 15,000 gallon fiberglass pool. ervery week the pool need chlorine. when i test its zero.

i add liquiud chlorine, 3" tablets w/shock and last week i added 2lb of shock.

PH is always 7.5

any idea why its using so much clorine?

thansk,

[Aramei]

I'm having the same issues. Do you cover your pool? Add the liquid at night? Do you have CYA (stabilizer/conditioner)?

[PaulR]

Chlorine is one of those things that you need to keep adding. It will be used up as it sanitizes the pool, kills organics (such as algae), and even UV rays from the sun. It's not uncommon to use 2-3ppm per day, and depending on your CYA level it could easily be more.

The 3" tablets have both chlorine and stabilizer, which will help protect the chlorine from sunlight. But you don't want too much stabilizer because it can make the chlorine less effective. The stabilizer doesn't get used up when the chlorine gets used up; the stabilizer stays around basically forever. So, you can use the tablets for a while, but should not use them long-term.

--paulr

[Romulous]

I have just gone through this problem. It could be nitrogen. Nitrogen EATS chlorine like there is no tomorrow. I only realized this problem when my solar blanket well 2 of them literally deflated and sunk to the bottom of the pool as the bubble inverted and deflated themselves. These were 2 brand new covers so it was the pool water, one was on for two days only. No pool company here could figure out the problem as the water appeared clear, until I found an obscure reference to why the bubbles deflated on the internet.

"The most common sanitizer used in swimming pools is chlorine. When added to pool water chlorine carries out two main functions; primarily it destroys micro-organisms but it also acts as an oxidizer, destroying organic contaminants. One result of these chemical processes is to convert the active free chlorine into chloramines and other combined chlorine compounds. It is recommended that free chlorine levels should be kept as low as possible – between 1 to 3 ppm. Combined chlorine levels must be below 0.5 ppm. Should this ratio be allowed to reverse and the combined chlorine levels climb above the levels of free chlorine, then nitrogen trichloride gas is produced. A clear indication of this condition is an obvious chlorine smell and it will also cause eye irritation to swimmers.

Extensive tests have been carried out and the resulting factors of this condition indicated that in a relatively short time the air inside the bubbles was almost completely drawn out. It is believed that when nitrogen trichloride gas is allowed to build up under the cover, air will diffuse out of the bubbles causing them to deflate. Once the bubbles have collapsed it is not possible to reverse the process and a new cover will be required.

When this problem occurs it is very important to bring back the pool water to an acceptable level of chlorination, either by shock dosing and burning out the high levels of combined chlorine, or carrying out a partial water change before a replacement cover is introduced onto the pool. When shock dosing the pool water it is essential to remove all covers until acceptable chlorine levels are reached. The pool water must then be closely monitored to ensure that the combined chlorine levels are kept below 0.5 ppm."

The Pool company here was able to do their test and if you have one of the big test kits you can do it yourself when you have the three step chlorine test. You need to make sure the the Combined Chlorine is lower than the Total Chlorine. The way we fixed this was to shock the pool with 20 litres of liquid chlorine and then test the next morning. I guess the goal is to have the chlorine levels stay high for 2 days, if that happens you have the problem licked! The pool company here said that it could take from 20 - 140 litres of liquid chlorine to fix the problem but trust me that is better than a full empty and refill!

Don't worry I felt like a fool too every time I went to the Pool store and got told their was no chlorine in the pool. As PaulR states Chlorine is something that does have to be added regularly but if you have nitrogen you could put 5 litres (my normal Sunday night shock dose) in the pool and have a reading of zero 12 hours later.

Hope this helps because I know it had stumped me for awhile and the new covers were getting expensive!

[Prostang]

I have just gone through this problem. It could be nitrogen. Nitrogen EATS chlorine like there is no tomorrow. I only realized this problem when my solar blanket well 2 of them literally deflated and sunk to the bottom of the pool as the bubble inverted and deflated themselves. These were 2 brand new covers so it was the pool water, one was on for two days only. No pool company here could figure out the problem as the water appeared clear, until I found an obscure reference to why the bubbles deflated on the internet.

"The most common sanitizer used in swimming pools is chlorine. When added to pool water chlorine carries out two main functions; primarily it destroys micro-organisms but it also acts as an oxidizer, destroying organic contaminants. One result of these chemical processes is to convert the active free chlorine into chloramines and other combined chlorine compounds. It is recommended that free chlorine levels should be kept as low as possible – between 1 to 3 ppm. Combined chlorine levels must be below 0.5 ppm. Should this ratio be allowed to reverse and the combined chlorine levels climb above the levels of free chlorine, then nitrogen trichloride gas is produced. A clear indication of this condition is an obvious chlorine smell and it will also cause eye irritation to swimmers.

Extensive tests have been carried out and the resulting factors of this condition indicated that in a relatively short time the air inside the bubbles was almost completely drawn out. It is believed that when nitrogen trichloride gas is allowed to build up under the cover, air will diffuse out of the bubbles causing them to deflate. Once the bubbles have collapsed it is not possible to reverse the process and a new cover will be required.

When this problem occurs it is very important to bring back the pool water to an acceptable level of chlorination, either by shock dosing and burning out the high levels of combined chlorine, or carrying out a partial water change before a replacement cover is introduced onto the pool. When shock dosing the pool water it is essential to remove all covers until acceptable chlorine levels are reached. The pool water must then be closely monitored to ensure that the combined chlorine levels are kept below 0.5 ppm."

The Pool company here was able to do their test and if you have one of the big test kits you can do it yourself when you have the three step chlorine test. You need to make sure the the Combined Chlorine is lower than the Total Chlorine. The way we fixed this was to shock the pool with 20 litres of liquid chlorine and then test the next morning. I guess the goal is to have the chlorine levels stay high for 2 days, if that happens you have the problem licked! The pool company here said that it could take from 20 - 140 litres of liquid chlorine to fix the problem but trust me that is better than a full empty and refill!

Don't worry I felt like a fool too every time I went to the Pool store and got told their was no chlorine in the pool. As PaulR states Chlorine is something that does have to be added regularly but if you have nitrogen you could put 5 litres (my normal Sunday night shock dose) in the pool and have a reading of zero 12 hours later.

Hope this helps because I know it had stumped me for awhile and the new covers were getting expensive!

This sounds like what I have been experiencing. The only issue I have with the above information is that when I have my water tested at the pool store, the chlorine flashes a color and the turns clear (appears that no chlorine is present in the water). The pool store owner had me take out my floating chlorine tablet dispenser for five days. We then retested the water and it was within the desired ranges. I still continue to lose pool covers.

[chem geek]

If they are using a DPD chlorine test, then flashing a color and turning clear means that the chlorine level is very high, above 10 ppm FC. The same can be true of the FAS-DPD chlorine test in which case you simply add more powder (with DPD you can't do anything except dilute the water sample first). This is very different than the situation described where the chlorine gets used up quickly by ammonia in the water (the oxidation of which can produce nitrogen trichloride, in the pool cover example of deterioration of the bubbles).

[Prostang]

I just got back from the pool store. I went with several prints from this forum with many questions and a sample of water to test. My chemicals are within desired ranges:

Free Chlorine 8.5ppm

Total Chlorine 8.5ppm

pH 7.4

Hardness 120ppm (I have added to compensate for the low number)

Alkalinity 104ppm

Syanuric Acid 20ppm

Total Dissolved Solids 600ppm

Nitrate 2.00ppm

The fact that my Total=Free tells me that Combined is 0 and not what a couple of other posts are experiencing. Could it be our water softener that is causing me this headache? At startup this year, I almost did a complete water change. I had maybe 1.5 feet of water in a 15' round, 48" high pool.

Any help is greatly appreciated.

[chem geek]

If the main issue you have is rapid degradation of pool covers, then I would say that is due to the combination of a high FC with a low CYA along with likely having low pH at times due to use of Trichlor pucks/tabs which are very acidic. To prevent algae growth, you only need a Free Chlorine (FC) that is at least a minimum of 7.5% of the Cyanuric Acid (CYA) level. You should probably raise your CYA to at least 30 ppm and then have the FC not get above 4-5 ppm, assuming you can make sure it doesn't get below 2.2 ppm.

[Prostang]

If the main issue you have is rapid degradation of pool covers, then I would say that is due to the combination of a high FC with a low CYA along with likely having low pH at times due to use of Trichlor pucks/tabs which are very acidic. To prevent algae growth, you only need a Free Chlorine (FC) that is at least a minimum of 7.5% of the Cyanuric Acid (CYA) level. You should probably raise your CYA to at least 30 ppm and then have the FC not get above 4-5 ppm, assuming you can make sure it doesn't get below 2.2 ppm.

Thanks Chem Geek. I will print this and give it a shot. By chance, does a large (cometimes two) bubble between the water and the cover have to do with the nitrogen levels? Last year every pool cover I bought would sink. This year, they are staying afloat. They still lose air in every single cell, but they stay afloat and often have at least one pocket of air under it?

[chem geek]

I honestly don't think the problem you were having was excessive chloramines or nitrogen trichloride. I think it was just high chlorine levels and possibly acidity if you were using Trichlor. If you get yourself a good test kit that has a FAS-DPD chlorine test, such as the Taylor K-2006 or the TF100 from tftestkits.net, then you will be able to measure Free Chlorine (FC) and Combined Chlorine (CC) to within 0.2 ppm. Read the Pool School for more info on how to maintain your pool.

[speedjunkie]

I just got back from the pool store. I went with several prints from this forum with many questions and a sample of water to test. My chemicals are within desired ranges:

Free Chlorine 8.5ppm

Total Chlorine 8.5ppm

pH 7.4

Hardness 120ppm (I have added to compensate for the low number)

Alkalinity 104ppm

Syanuric Acid 20ppm

Total Dissolved Solids 600ppm

Nitrate 2.00ppm

The fact that my Total=Free tells me that Combined is 0 and not what a couple of other posts are experiencing. Could it be our water softener that is causing me this headache? At startup this year, I almost did a complete water change. I had maybe 1.5 feet of water in a 15' round, 48" high pool.

Any help is greatly appreciated.

My pool store told me that nitrates were bad. At 2.0ppm, that looks bad to me. Nitrates will for sure eat chlorine, I'd look at that being a problem. I believe they said anything over .5ppm was trouble.

Mike

[chem geek]

Mike,

Your pool store is giving general advice without any understanding of what nitrates and phosphates really do.

Nitrates as well as phosphates do NOT "eat" chlorine -- they do not chemically react with chlorine nor are they a catalyst in any chlorine degradation. Nitrates and phosphate are necessary nutrients for algae growth. That's all. So if you don't control the algae, then chlorine will get consumed by growing algae and initially the algae growth isn't visible so this looks like an unusual chlorine demand. However, algae does not grow faster and faster and faster with more and more nitrates and phosphates. Algae growth rates are also limited by temperature and sunlight. And most importantly, algae growth can be controlled by chlorine alone.

My pool (shown here) has 2000-3000 ppb phosphates and I'm sure the nitrates are high as well since fertilized soil sometimes gets blown in and yet my pool is free of algae growth because I maintain the proper Free Chlorine (FC) level relative to the Cyanuric Acid (CYA) level. There are also others at Trouble Free Pool with even higher phosphate and nitrate levels that are miraculously able to maintain their pools with chlorine alone.

Also, don't mix up what was said in the post about "nitrogen" which in the details of the post was "nitrogen trichloride" with nitrates since they are not the same at all. Nitrogen trichloride is a disinfection by-product produced when chlorine oxidizes ammonia and nitrogen-containing organic compounds. Higher active chlorine levels lead to higher nitrogen trichloride production, but if one has the proper FC/CYA ratio in their pool then this amount is very low. The earlier poster had a very high FC/CYA ratio with FC of 8.5 and CYA of 20 ppm at a pH of 7.4 which is almost 10 times the active chlorine level that is normally recommended (a minimum FC that is at least 7.5% of the CYA level, but not more than 15% of the CYA level). There is no mystery here. Chlorine slowly degrades covers and having nearly 10 times the active chlorine level will degrade the cover that much faster!

One can certainly do a partial drain/refill of their pool water to lower nitrate levels and one can buy expensive phosphate removers to lower phosphates and one can buy algaecide to prevent algae growth and can shock the pool regularly, but all of this is unnecessary if you simply maintain the appropriate FC/CYA ratio since chlorine alone can prevent algae from growing even when it has all the nutrients it could possibly want.

Richard

[speedjunkie]

Mike,

Your pool store is giving general advice without any understanding of what nitrates and phosphates really do.

Nitrates as well as phosphates do NOT "eat" chlorine -- they do not chemically react with chlorine nor are they a catalyst in any chlorine degradation. Nitrates and phosphate are necessary nutrients for algae growth. That's all. So if you don't control the algae, then chlorine will get consumed by growing algae and initially the algae growth isn't visible so this looks like an unusual chlorine demand. However, algae does not grow faster and faster and faster with more and more nitrates and phosphates. Algae growth rates are also limited by temperature and sunlight. And most importantly, algae growth can be controlled by chlorine alone.

My pool (shown here) has 2000-3000 ppb phosphates and I'm sure the nitrates are high as well since fertilized soil sometimes gets blown in and yet my pool is free of algae growth because I maintain the proper Free Chlorine (FC) level relative to the Cyanuric Acid (CYA) level. There are also others at Trouble Free Pool with even higher phosphate and nitrate levels that are miraculously able to maintain their pools with chlorine alone.

Also, don't mix up what was said in the post about "nitrogen" which in the details of the post was "nitrogen trichloride" with nitrates since they are not the same at all. Nitrogen trichloride is a disinfection by-product produced when chlorine oxidizes ammonia and nitrogen-containing organic compounds. Higher active chlorine levels lead to higher nitrogen trichloride production, but if one has the proper FC/CYA ratio in their pool then this amount is very low. The earlier poster had a very high FC/CYA ratio with FC of 8.5 and CYA of 20 ppm at a pH of 7.4 which is almost 10 times the active chlorine level that is normally recommended (a minimum FC that is at least 7.5% of the CYA level, but not more than 15% of the CYA level). There is no mystery here. Chlorine slowly degrades covers and having nearly 10 times the active chlorine level will degrade the cover that much faster!

One can certainly do a partial drain/refill of their pool water to lower nitrate levels and one can buy expensive phosphate removers to lower phosphates and one can buy algaecide to prevent algae growth and can shock the pool regularly, but all of this is unnecessary if you simply maintain the appropriate FC/CYA ratio since chlorine alone can prevent algae from growing even when it has all the nutrients it could possibly want.

Richard

As usual, good info Richard! Thanks!

Mike