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Thread: How much Active Chlorine will damage heater?

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    How much Active Chlorine will damage heater?

    Quote Originally Posted by chem geek View Post
    So this effectively makes the chlorine level 2-3 ppm FC higher at the heater than it otherwise would be. With CYA in the water, the active chlorine level will still be low but perhaps would be equivalent to 0.14 ppm FC with no CYA instead of 0.08 ppm FC with no CYA. The reason Trichlor pucks in the skimmer are a problem is that when the pump is off they build up high chlorine AND low pH which then gets blasted to the heater on every pump cycle. Low pH is far more harmful to heaters than chlorine unless the FC level is very high and there is no CYA (i.e. a very high active chlorine level).

    Now an SWCG cell may output only somewhat higher FC since it's on-time is probably not 100% (but 50% on-time would be double the FC compared to The Liquidator, all else equal), but the reason it is put after the heater isn't only because of this higher FC level but that part of the water from the cell is very acidic while other parts are very basic. So unless the water coming out of the cell was thoroughly mixed together, one part of the stream will be very acidic and at a high chlorine level which is a bad combo. By the time such water comes out of the returns, it gets mixed with the bulk water so is not a problem.
    Let's say the pH were maintained at 7.5 at all times for 100% of the water.

    How much Active Chlorine would it take to damage the heater?

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    Re: How much Active Chlorine will damage heater?

    Chlorine really isn't an issue for copper at any of the levels you might encounter in a pool, and if you have any CYA at all the chlorine levels can be dramatically higher that you would use in a pool and you still won't have any corrosion. I don't know what happens at concentrations several orders of magnitude higher however, but regardless this isn't relevant to pools.
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    Re: How much Active Chlorine will damage heater?

    The reason I ask is an acquaintance of mine in the industry drained a pool managed by another company because the pool builder said "the chlorine is too high". I think it was around 20-25 ppm. If I remember correctly, it was a trichlor tab pool. No one seemed to know what the cyanuric acid level was.

    This is the same builder that wants to keep the pH at 7.0 as much as possible to "keep the plaster looking fresh". He likes dark surfaces. He seems to never mention the Calcium Saturation Index, only the pH.

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    JasonLion's Avatar
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    Re: How much Active Chlorine will damage heater?

    PH below 6.8 is a serious problem for copper. I suspect that keeping the PH around 7.0 involves letting it go below 6.8 fairly regularly. And of course his plaster isn't going to last all that long.
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    Re: How much Active Chlorine will damage heater?

    Quote Originally Posted by JasonLion View Post
    PH below 6.8 is a serious problem for copper. I suspect that keeping the PH around 7.0 involves letting it go below 6.8 fairly regularly. And of course his plaster isn't going to last all that long.
    Thankfully, most of his pools require manual doses of acid. Although it could be a problem if the tech were to intentionally go below 7.0 to average the daily pH levels at 7.0. Also, most of his pools are negative edge. The pH seems to rise faster than non-negative edge pools due to the aeration I suppose.

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    Re: How much Active Chlorine will damage heater?

    The pH rises not only due to the increased aeration, but having the pH be low accelerates that as well. So does a high TA. You can see from this table how much a pool is over-carbonated and how this over-carbonation goes up dramatically as the pH is lowered and as the TA is raised.

    So maintaining such a low pH will require a lot more chemical addition since one would need to add acid to keep the pH low and need to add baking soda to maintain the TA. Also, as Jason noted, the low pH is the worst thing for metal corrosion. With CYA in the pool, one shouldn't worry about the chlorine level being an issue for corrosion, but the low pH is more of an issue. After all, this is the primary reason tap water is usually above 7.5 and often closer to 7.8 to 8.0 in pH -- it's the primary way such corrosion is prevented (some municipalities also add corrosion inhibitors, including phosphates). Municipalities used to use chlorine at around 1-2 ppm FC (max. EPA limit is 4 ppm FC), but now many use monochloramine instead also at around 1-2 ppm (again a max EPA limit of 4 ppm). These levels are higher than the active chlorine level in pools with CYA.

    That pool builder that drained a pool with 20-25 ppm FC because the chlorine level was too high was ignorant on multiple fronts. First, if there was CYA in the water, which there should have been given it was a Trichlor pool, then the active chlorine level wasn't that high. Second was that one doesn't have to drain a pool to lower the chlorine level -- one can simply add a dechlorinator (reducing agent). On the other hand, if the pool had a high CYA level, then draining did the customer a favor to start off again with a low CYA level giving more room for the CYA to climb given that it's a Trichlor pool.
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