no chlorine

Chlorinating, maintaining the right chlorine levels, chlorine problems. Dichlor, trichlor, cal hypo, bleach, granules, chlorine pucks or sticks.

Postby pool person » Tue 09 Sep, 2008 20:50

ive tried my method of the ten times amount of chlorine you normally use on 1000's of customers who live near farms and it gets rid of nitrates and phosphates.
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Postby chem geek » Tue 09 Sep, 2008 21:53

I'm sorry, but chlorine does NOT get rid of nitrates and phosphates. Chlorine does not react with them. Chlorine will prevent algae growth in spite of nitrates and phosphates being present. Are you measuring both nitrates and phosphates with a test kit? How do you know that nitrates and phosphates are lowered after shocking with chlorine?

I've done bucket tests with high phosphate water 2000-3000 ppb, added high chlorine levels, and not seen the phosphate level drop after giving it time for the chlorine level to get lower (to prevent any interference with the test).
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Postby pool person » Wed 10 Sep, 2008 11:30

im telling you if a 20,000 gallon pool has a nitrate reading of 10-15ppm i say to dump in 3 five gallon drums of liquid chlorine. they come back and the nitrates are gone.. i even did a test and i said do 2 five gallon drums and it didn't work. i have been doing this method for about 5 years now and have no complaints. how else would u get rid of nitrates.. empty and refill?
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Postby chem geek » Wed 10 Sep, 2008 13:00

Yes, getting rid of either phosphates or nitrates would normally require dilution of the water or in the case of phosphates you can use lanthanum chloride which is in phosphate removers that will precipitate lanthanum phosphate (that you then vacuum to waste). However, getting rid of phosphates and nitrates is not normally necessary (more on that below).

Nitrates cannot be oxidized (by chlorine or any other oxidizer) since the nitrogen is already in the highest +5 oxidation state, but it can be reduced in acidic conditions but that doesn't happen in pools. However, your experience is real so I'll have to look for what mechanism could be happening. I assume you do the post-shock nitrate test after the FC levels have dropped; otherwise the high chlorine levels may interfere with the nitrate test.

Adding 3 5-gallon drums of chlorinating liquid, that I assume to be 12.5%, in 20,000 gallons would raise the FC by 94 ppm which is, of course, extraordinarily high. This could accelerate oxidation of Cyanuric Acid since that can occur at high FC levels at high pH (which would occur from adding lots of chlorinating liquid).

The thing is that both nitrates and phosphates are required algae nutrients. If you remove either one then algae will not grow. So even in a high nitrate pool, you could remove the phosphates with a phosphate remover and that would work as well as removing the nitrates, though could cost a lot since phosphate removers aren't cheap.

Nevertheless, why bother with lowering either phosphates or nitrates? If the Free Chlorine (FC) level is kept at least at 7.5% of the Cyanuric Acid (CYA) level, then algae will be killed faster than it can grow even with phosphates and nitrates present. I suspect that in many of the pools with algae that you deal with, the CYA level is high and the FC level isn't kept at least at 7.5% of the CYA level. Your super-high-shocking may lower the CYA level without requiring dilution and that would certainly help the situation, but it would have nothing to do with nitrates. Maybe high CYA levels give a false nitrate reading in the test -- I don't know about that.

I'll do some experiments with fertilizer and do some super-shocking to see if the nitrates truly get reduced somehow.

Richard
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Postby pool person » Wed 10 Sep, 2008 23:11

when I tell customers that they have to put in 3 five gallons of liquid chlorine i say they have a chlorine lock. Not only do i see a reading of nitrates in the water but normally there is a 6 or 7ppm of Total Chlorine and 0ppm free chlorine. thats when i use that method and it has worked every time. i have tried experiments of just keep shocking it normally for a straight week. all it does is just keep raising the total chlorine higher and higher and free chlorine still stays at zero. Normally the pool stays cloudy. I say hit it with the 3 five gallons and let it run for 24 hours and the next day pool is clear and the chlorine evens out with free and total making 0 combined chlorine. Sometimes the liquid shoots it up way high sometimes it sets it back to a zero zero reading. I say do a normal shocking and pool is clear for the rest of the summer.
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Postby chem geek » Thu 11 Sep, 2008 02:00

OK, now this makes much more sense. There really isn't "chlorine lock", but it does seem like it. What is happening is that the CYA level is high enough to make the chlorine less effective because the FC level wasn't raised to keep the FC/CYA ratio constant. So algae grows faster than chlorine can kill it which makes the water cloudy (it would eventually turn into a full-fledged algae bloom), the chlorine gets used up and forms Combined Chlorine (CC) and the high CYA level makes the oxidation of this CC very slow.

Adding lots of chlorine raises the FC high enough to accelerate the oxidation of the CC and the killing of algae faster than it can grow.

So that's perfectly explained. However, if the CYA level isn't lowered somehow, the situation can repeat itself unless the FC level is kept higher. So perhaps the high chlorine level also lowers the CYA level somewhat as well.

That's my best guess of the situation though it would not explain the before/after nitrate measurements.

Richard
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Postby pool person » Thu 11 Sep, 2008 15:18

alright i see.. I work at a pool store in Mt. Holly, New Jersey. Do you think you can explain the whole CYA/ FC ratio? I have worked there for quite some time now and me nor my boss know about the deal with high CYA and the ineffectiveness of chlorine. if you could either explain it or give me a link to a good site about it that would be great. and/or give me different pool situations with a problem with CYA And chlorine. Thanks
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Postby chem geek » Thu 11 Sep, 2008 17:24

Basically, the active form of chlorine is hypochlorous acid that does most of the disinfection killing bacteria, inactivating viruses, killing algae and oxidizes organics. Hypochlorite ion is far weaker by orders of magnitude, but most (about 97%) of what is measured as Free Chlorine (FC) is actually in the form of chlorine combined with Cyanuric Acid (CYA) in a series of compounds called chlorinated isocyanurates that are almost inert. They do not disinfect nor oxidize to any great extent. They do, however, release the chlorine as hypochlorous acid as this gets used up.

This post shows the traditional industry graph of hypochlorous acid concentration as a function of pH when there is no CYA and then shows the true graph when CYA is present. The NSPF CPO and APSP TECH courses don't teach this for whatever reason.

The amount of active chlorine, hypochlorous acid, is proportional to the FC/CYA ratio. So if you double the amount of CYA in the water, then you need to double the amount of FC to have the same level of disinfection, oxidation and algae prevention. It's easy to have CYA rise when using stabilized chlorine since the following are chemical facts independent of concentration.

For every 10 ppm FC added by Trichlor, it also increases CYA by 6 ppm.
For every 10 ppm FC added by Dichlor, it also increases CYA by 9 ppm.
For every 10 ppm FC added by Cal-Hypo, it also increases Calcium Hardness (CH) by 7 ppm.

The technical derivation for the FC/CYA ratio is described here and some qualitative descriptions are also found here in extracts from the original paper presented at a 1973 symposium and published in 1974.

The stabilized chlorine industry has been touting the mantra "CYA doesn't matter; only FC matters" for whatever reason and unfortunately this has also led to the belief that "CYA should not be used in indoor pools; it only protects chlorine from breakdown from sunlight" which is only a half-truth since it leaves out the significant fact that it reduces the active chlorine concentration. This means that pools without CYA, such as indoor pools, are over-chlorinated by orders of magnitude with 10-30 times the amount of hypochlorous acid concentration needed. This leads to much faster degradation of swimsuits (elasticity gets shot), flaky skin and frizzy hair as my wife experiences during the winter at a community center indoor pool while in our own pool during the summer there are none of these problems even after 5 years.

Richard
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High content of Phosphate and Nitrogen

Postby MunchaBunch » Sun 03 May, 2009 13:07

I went to the pool store and they claim I have a high content of Nitrogen (70 ppm) and Phosphate (2,500 ppm) in my swimming pool. It is very likely that fertilizer from my yard got in the pool. The store recommends that I drain the pool and filter. This would be an expensive venture as water rates have recently gone through the roof.
Will the nitrogen and phosphate levels reduce as time goes by or is this an ongoing ordeal that sooner or later I will have to drain the pool? Is this hazardous to swim in? :problem:
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Postby chem geek » Sun 03 May, 2009 18:07

Until recently, I had 2000-3000 ppb of phosphates in my pool (not sure what my nitrates level was) and have kept the pool free from algae growth through maintaining the proper FC/CYA ratio. I diluted my pool water with winter rains and didn't retest the phosphate level (I don't really care about it).

The nitrates and phosphates will lower over time with water dilution (NOT evaporation and refill, however, but by splash-out, backwashing, rain overflow, etc.). Evaporation and refill can actually increase phosphate levels as happens in my pool because 300-500 ppb phosphates are in the fill water (they are used for corrosion control by the water district). It is not hazardous to swim in.

You should read the articles in the Pool School and look at the Chlorine / CYA Chart to see what FC level you need for your CYA level to prevent algae growth. You can use 50 ppm Borates in the pool to help inhibit algae or you can use a weekly PolyQuat 60 algaecide or a phosphate remover, all at extra cost (the phosphate remover will be initially very expensive since the phosphate level is so high). If you use these supplements, then you can maintain a somewhat lower FC level. Otherwise, you need to follow the chart.

The biggest problem with a pool high in phosphates and nitrates is that it is rather unforgiving if you ever let the FC/CYA ratio get too low. Algae can grow quickly in such a pool so you need to watch your chlorine levels very carefully or use one of the supplemental products I mentioned. Also, realize that if you are using stabilized chlorine (Trichlor or Dichlor) then you are increasing your Cyanuric Acid (CYA) levels which makes the chlorine less effective. If the CYA is doubled at the same FC level, then the chlorine is half as effective and could kill algae slower than algae can reproduce at which point you get unusual chlorine demand, dull water and eventually cloudy and then green water from an algae bloom.

Richard
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