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Okay, it seems that most of the neighbors in the "hood" are having problems this summer getting their chemicals to balance out and achieving clear pool water. They all use well water. From reading in the forum sounds like they should try a metal out solution?? In particular, I have 1 neighbor who just refilled his pool, shocked it, and immediately it turned green. Can anyone help?? I have a feeling they don't believe in measuring appropriately for the gallons they have in the pool and feel that just pouring it in will do the trick -

Also - is is safe to swim in a pool with low chlorine levels - or no chlorine - even if the water is clear?? I tend to think not - but just want to know what someone else thinks.

Thanks in advance

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Okay, it seems that most of the neighbors in the "hood" are having problems this summer getting their chemicals to balance out and achieving clear pool water. They all use well water. From reading in the forum sounds like they should try a metal out solution?? In particular, I have 1 neighbor who just refilled his pool, shocked it, and immediately it turned green.

Sounds like copper!

Can anyone help?? I have a feeling they don't believe in measuring appropriately for the gallons they have in the pool and feel that just pouring it in will do the trick -

Not a good idea!

Also - is is safe to swim in a pool with low chlorine levels - or no chlorine - even if the water is clear?? I tend to think not - but just want to know what someone else thinks.

In a word....NO! The water is NOT sanitized and it can actually transmit illnesses! Clear water does NOT mean safe water!

Thanks in advance

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  • 4 months later...
  • 3 weeks later...

Okay, it seems that most of the neighbors in the "hood" are having problems this summer getting their chemicals to balance out and achieving clear pool water. They all use well water. From reading in the forum sounds like they should try a metal out solution?? In particular, I have 1 neighbor who just refilled his pool, shocked it, and immediately it turned green. Can anyone help?? I have a feeling they don't believe in measuring appropriately for the gallons they have in the pool and feel that just pouring it in will do the trick -

Also - is is safe to swim in a pool with low chlorine levels - or no chlorine - even if the water is clear?? I tend to think not - but just want to know what someone else thinks.

Thanks in advance

The most common metal that turns your water green after shock dosing is Iron. The home test for iron is to test the chlorine if it is reading at a reasonable level and the water is green most likely it is iron. To fix iron you need to add more chlorine, and lots of it. The iron has to be oxidised before the water will come clear. The usual practice is to shock it to 10-15 mg/l nightly and run the filter constantly. Nothing will change for several days then suddenly the water will be crystal clear.

You can swim in water with chlorine as low as you like, however chlorine is there to protect you and your family from bacteria build up. Bacteria is introduced to the pool from a myriad of sources including from the bather themselves. Depending on temperature you may want to increase or decrease your chlorine level, but should probably not go below 1.5 mg/l for safe bathing.

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The most common metal that turns your water green after shock dosing is Iron.

Actually, copper is what will turn the water green after shocking. Iron will turn it yellow to brownish, depending on the iron concentration! Manganese will cause a purple coloration. The reason the water colors is because the oxidation state of the metal ions in the water is changed by the chlorine (oxidizing agent). By raising the pH and the oxidizer level it is possible to cause the metals to precipitate out of solution but it is not a recommended procedure unless you REALLY understand the chemistry that is going on.

The home test for iron is to test the chlorine if it is reading at a reasonable level and the water is green most likely it is iron. To fix iron you need to add more chlorine, and lots of it. The iron has to be oxidised before the water will come clear. The usual practice is to shock it to 10-15 mg/l nightly and run the filter constantly. Nothing will change for several days then suddenly the water will be crystal clear.

In theory this practice will work by causing the metals to precipitate out of solution and get filtered out but in actual practice what usually happens is that the metals deposit in the pool as stain, which is a more difficult problem to deal with!. The pH has to be closely monitored for this to work and the chlorine needs to be introcduced slowly into the skimmer so the staining will occur in the filter and not on the pool surfaces. It is a risky procedure at best!

You can swim in water with chlorine as low as you like, however chlorine is there to protect you and your family from bacteria build up. Bacteria is introduced to the pool from a myriad of sources including from the bather themselves. Depending on temperature you may want to increase or decrease your chlorine level, but should probably not go below 1.5 mg/l for safe bathing.

Most state health departments now say that chlorine levels should not go under 2 ppm and allow swimming up to 10 ppm for both pools and hot tubs. I personally would not go swimming if the chlorine levels were not adequite for proper sanitation. Just because the water looks clear and clean does not mean it is safe to swim in. It could contain a very high bacteria count and could cause illness.

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Most state health departments now say that chlorine levels should not go under 2 ppm and allow swimming up to 10 ppm for both pools and hot tubs. I personally would not go swimming if the chlorine levels were not adequite for proper sanitation. Just because the water looks clear and clean does not mean it is safe to swim in. It could contain a very high bacteria count and could cause illness.

Waterbear, please find out who you are talking to before going off on a tangent. I was speaking about a backyard pool not a commercial pool. I would point out I helped write the code for the health department.

Whilst copper can cause green water, Iron normally causes green water as the brown colour you are referring to normally reflects with the blue pool to create a greenish tinge. In addition when iron is present an odd reaction occurs where algal growth accelrates on contact with chlorine inside the iron matrix. Perhaps once you have another fifteen years experience you will have treated some pools with cast iron pipework and will see this phenomenon.

If you have metals dropping out of solution when using EDTA based product I would suggest you seriously invetigate the filter rate. As across four countries in more years than I carre to recall I have not seen this in every kind of water you care to name.

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Waterbear, please find out who you are talking to before going off on a tangent. I was speaking about a backyard pool not a commercial pool. I would point out I helped write the code for the health department.

Water borne illness can occur just as easily in a residential pool as in a commercial pool. Proper sanitizer levels are important in either! On the same note, such things as cyanuric acid levels, which most state health departments limit to a max of 100 ppm, are allowed to rise to levels well beyond that in residential pools and cause the owners no end of problems with algae blooms and possible damage to plaster finishes! Good pool maintenance is good pool maintenance, whether in a commercial or residential pool, don't you agree?

Whilst copper can cause green water, Iron normally causes green water as the brown colour you are referring to normally reflects with the blue pool to create a greenish tinge.

Not all pools are finished in a blue color these days, most fiberglass pools are white and the aggregate finishes come in a variity of colors. I was wondering if you were referring to the yellow water and blue finish causing the water to look green when I read your post but I stand by what I posted (and you just acknowledged it) that iron causes a yellow to brown color in the water.

In addition when iron is present an odd reaction occurs where algal growth accelrates on contact with chlorine inside the iron matrix. Perhaps once you have another fifteen years experience you will have treated some pools with cast iron pipework and will see this phenomenon.

Green water (or yellow water) from oxidized metals is an entirely different story then green water caused by algael blooms and needs to be treated differently. It is important to determine which is causing the problem. Algae will usually also cause the water to cloud while metals will color the water yet it remains clear. Also, if the color develops immediately after shocking then metals would be the suspect.

If you have metals dropping out of solution when using EDTA based product I would suggest you seriously invetigate the filter rate. As across four countries in more years than I carre to recall I have not seen this in every kind of water you care to name.

The majority of metal sequesterants on the market are HEDP based, not EDTA based. In fact, I only know of one personally that is EDTA based and that is NaturalChemistry's MetalFree (although there may be some others). The big ones (Jack's Magic, ProTeam MetalMagic, Advantis Metal Gon, and the vast majority of private label and white bottle products) are HEDP based or similar phosphonates.

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  • 2 weeks later...

This is a great discussion. By now I hope things have improved for annwithoutanE.

It sounds like there is a water chemistry problem. Without a good set of tests, it is just shooting in the dark. Taking a water sample in for testing and/or getting a quality test kit will get things going on the right track. Then implement the corrections in steps to allow the water to “balance” (a day to a week on infrequent drastic changes).

It is important to keep in mind that most pool test procedures are accurate (easily repeatable with results within an acceptable range) but not precise (it is just not that critical – close is good enough in horseshoes, hand grenades, and pool chemistry). I took the same sample of water to three different pool retailers within one hour of being drawn and found that most came up with similar opinions and recommendations about the water but their “values” were not consistent. For comparison, I also tested the same water for the big three (chlorine, Ph, and alkalinity) myself with my chemical kit and test strips, and I had slightly different results too. The biggest difference from the “professionals” was in conditioner, some had me adding while others said I almost had too much. Now I always test at least twice if anything looks unusual or there is a visible water problem.

Here are my thoughts about chlorine (sanitizer)…there should be an adequate amount of free-available chlorine to have a good chance of killing any harmful “bugs” that get into the pool within a reasonable amount of time. My chlorinated city water does not even register with a standard pool chemistry test, but would never think twice about letting my kids share a bath. Also, with the popularity of spa tubs, I would bet there are many adults with similar thoughts.

Personal hygiene is another factor in the “when to swim” equation. If I would feel comfortable letting my kids use the person’s bathroom and sit on the toilet seat, I’m probably going to swim in their pool (or be a guest in my pool). If the swimmers are typically in good health and utilize the bathroom instead of the pool, most backyard swimming pools are much less likely to spread disease than Southern California beaches.

I’m not saying to ignore the chlorine level, but you have to remember it is taken at a snapshot in time. In the morning before my salt-chlorine generator has gotten working (I have solar heating so my pump runs during daylight hours) the chlorine level is likely to be “low.” After a day of moderate pool use, the chlorine level is likely to be “acceptable.” Just before a swim party on a hot summer day I typically bump the chlorine and/or use a non-chlorine shock to increase the probability of free-available chlorine. After the party the chlorine may be at “zero” but it is still likely to be “safe” for an evening dip.

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  • 2 weeks later...

waterbear, I believe the CT that dynamictiger is referring to is the standard product of chlorine concentration (in mg/liter or ppm) times the contact time (in minutes) and this product is approximately a constant at a given pH and for a given species of bacteria/protozoa/virus to be killed.

dynamictiger, the standard CT tables refer to chlorine concentration without the presence of Cyanuric Acid (CYA). The values vary by pH with lower CT at lower pH because it is generally the hypochlorous acid, HOCl, form of chlorine that is effective as a disinfectant and not the hypochlorite ion, OCl-, form. What you may not be aware of is that in the presence of CYA, the amount of HOCl drops dramatically. A rough rule of thumb that applies at a pH of 7.5 and when the CYA ppm is at least 5 times the FC ppm is that the concentration of the active form of chlorine (HOCl) is reduced by a factor that is 75% of the CYA concentration in ppm. So at 30 ppm CYA, this means that the effective chlorine concentration (i.e. the number you use in the "C" part of CT) is reduced by a factor of 22.5 (in the example below, it's even worse at a factor of 34.5 -- I'll have to check if I need to change the rule of thumb, but the numbers below are accurately calculated and not from any rule of thumb).

At the standard recommended NSPI values of pH 7.5, TA 100, FC 3, CYA 30, CH 300, TDS 550, Temp 80F, the concentration of the active form of chlorine (HOCl) is only 0.042 ppm (this is ppm in chlorine gas, Cl2, units as is standard with all chlorine measurements). Without the CYA, the active form of chlorine would be at 1.45 ppm or about half of the FC which is to be expected at a pH of 7.5. Now before you get too shocked from this info let me tell you what this roughly corresponds to in ORP terms. This roughly corresponds to an ORP of 690 mV. The standard ORP minimum requirement for disinfection in commercial pools in the U.S. is 650 mV (in Germany it's much higher at 750 mV) which roughly corresponds to about 0.013 ppm or an FC of 1.0 when the CYA is 30. However, this 650 mV ORP level for disinfection is lower than that required to kill "hard-to-kill" bugs (including the bacteria Pseudomonas aeruginosa that causes "hot tub itch") which is partly why CYA is not recommended for hot tubs. The 650 mV level is also lower than needed to prevent most algae. Data from users on another forum seem to indicate that at least 0.03 and usually about 0.05 ppm HOCl is needed to prevent green algae. Even higher levels, perhaps 0.07 ppm HOCl, is needed to prevent regrowth of established black algae. For shocking green algae, a minimum of 0.3 ppm HOCl seems to be required while mustard/yellow (and possibly black) algae may need 1.0 ppm HOCl. Though this does not sound like a lot of chlorine, and indeed it isn't very much if no CYA is used, it takes a LOT of chlorine to achieve these levels in the presence of CYA. Even with 30 ppm CYA, it takes about 12 ppm FC to achieve shock level for green algae and 21 ppm FC to achieve shock level for mustard/yellow (and possibly black) algae. If you didn't have CYA, it would only take about 0.6 ppm and 2.1 ppm respectively.

I have all sorts of graphs and charts as well as a spreadsheet that computes the details of pool water chemistry, but it's on another forum and the rules of this forum seemed to imply that due to competitiveness no links should be made to other such forums (it didn't specifically forbid that, but it did say that those that run other forums couldn't post here; I don't run any forum, but don't want to violate the rules either).

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Chemgeek,

Thank you for clearing that up for me. I did not make the somwhat out of context connection because I was discussing (and thinking of) the thread topic of a pool that turned green immediately after shocking and had 'metals on the brain' so to speak :P . You actually answered it much better than I could and did bring up the important point that the presence of CYA in the equation alters things considerably from how it is normally presnented (or even thought of in the industry)! Excellent!

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  • 7 months later...

I am very impressed with the information provided in this thread. I wish I had found this a few weeks ago before draining my pool out of desperation. My pool color is caribbean blue pebble tec which is a green-blue color. My pool's readings required a shock treatment which was nothing out of the ordinary. I noticed the local water company working on their equipment the same week I shocked my pool. Within days, my pool turned green full of algea and no visability of the bottom.

I cleaned the filters daily, and continually ran it, no swimming, after running out of money, I added clorox bleach, and I even tried Tide detergent (cold water formula). The Tide improved it but not enough so I drained the pool.

I scrubbed down the pool, I used my shop vac to sucked out all the horrible gross green stuff that was in the pool & solar water lines. I then flushed the lines with clean water.

ITwo days ago, I filled the pool with water. I've added liquid chlorine but the pool rchlorine level reads nothing. I'm afraid to shock for fear of waking up to a green pool.

I plan on using the spreadsheet link to help me. I need recommendations on how to prevent another episode of shock enduced algae growth caused by high levels of IRON. If it happens again, you mentioned large amounts of chlorine. are necessary. Can you define "large amounts" (i.e., n times the amount needed for shock or for maintenance??), type of chlorine, liquid or dry?

My chlorine measures none at this time, is there any recommendation as to type of chlorine and procedure in this particular senerio.

Why couldn't I've born as smart as you? It's not easy not knowing.

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