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Thread: Adding salt-corrosion?

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    guamguy's Avatar
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    Adding salt-corrosion?

    I have been toying with the idea of adding salt to my pool for improved water feel. Today I removed my pool lights to fix a leak and discovered one of the Pentair light fixtures had a label on it stating "fresh water use only". Does this mean I can't use salt? I'm only looking to use about 1500-2000ppm.
    12,800 gallon IG plaster kidney-shaped pool, waterslide, 800 gallon spa.
    1HP 2 speed Sta-Rite pool pump, 1.5 HP Sta-Rite spa jet pump. 2 skimmers, 1 main drain
    Purex-Triton TR-60 325 lb.sand filter. 2" Plumbing, Intex SWCG, TF-100 test kit.
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    Mod Squad Bama Rambler's Avatar
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    Re: Adding salt-corrosion?

    Those warnings are usually for true salt water pools (35000 ppm) and don't include the low levels seen in a SWCG pool. However, it would be best to contact the mfg of the light and ask the direct question of them. They'll be your best source.
    Dave J. TFP Moderator
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    Re: Adding salt-corrosion?

    When they say Fresh water, they mean don't use in sea water pools, such as those on a passenger liner or an oceanside aquatic facility that uses water from the ocean.

    I assume you bonded the pool when you built it. As added insurance, you can add a sacrificial zinc anode to help prevent electrolytic corrosion.

    Pentair lights use a high quality stainless for the fascia ring so in salted fresh water pools, it isn't an issue.

    Scott
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    guamguy's Avatar
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    Re: Adding salt-corrosion?

    I am assuming the pool was bonded when built. I'm not sure, as the pool came with the house. Where would I add a zinc or 2? Should they be in the light niches?
    12,800 gallon IG plaster kidney-shaped pool, waterslide, 800 gallon spa.
    1HP 2 speed Sta-Rite pool pump, 1.5 HP Sta-Rite spa jet pump. 2 skimmers, 1 main drain
    Purex-Triton TR-60 325 lb.sand filter. 2" Plumbing, Intex SWCG, TF-100 test kit.
    Link to pics of my pool! http://www.troublefreepool.com/my-oasis-t26558.html

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    Re: Adding salt-corrosion?

    A sacrificial anode is ideally buried in moist soil and electrically connected to the bonding wire. It will then protect everything that is connected to that bonding wire. The sacrificial anode will need to be replaced every so often, usually every 1-3 years but the frequency depends on the specifics of the pool components (and the size of the anode).
    16,000 gallon outdoor in-ground 16'x32' plaster pool; Pentair Intelliflo VF pump; Pentair IntelliTouch i9+3s control system; Jandy CL-340 square foot cartridge filter
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    Re: Adding salt-corrosion?

    Re - anode:

    I've seen zinc disks in skimmers that supposedly do the same thing. Is it true? (the disk is in the water which is in contact with some part of the bonding, is that OK?)
    Luv& Luk
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    Re: Adding salt-corrosion?

    Quote Originally Posted by waste
    I've seen zinc disks in skimmers that supposedly do the same thing. Is it true? (the disk is in the water which is in contact with some part of the bonding, is that OK?)
    No, this doesn't work. The idea of a sacrificial anode is to connect it electrically (i.e. with conductive wire) to the bonding wire such that it puts a negative charge on the wire and all attached metal exposed to water in order to inhibit corrosion since it creates a greater potential to overcome for such corrosion (think of the negative charge as holding the neutral metal atoms more firmly in place preventing them from forming positive ions separating from some of their electrons). Putting a zinc block in the skimmer would just tend to corrode the zinc block adding zinc to the water that could eventually stain. It won't slow down corrosion with other metal in the pool. Chlorine (and dissolved oxygen) would simply oxidize the zinc block, but would continue to oxidize other metal in the pool as well.

    In a somewhat real sense it's like a chemical equilibrium where the metal half-reaction is as follows:

    Fe(s) --> Fe2+ + 2e- ..... E0 = +0.447V

    and where the negative charge produces a surplus of electrons (or an electromotive force of providing more electrons) that makes it more difficult for the above reaction to proceed. The zinc sacrificial anode has the following half-reaction:

    Zn(s) --> Zn2+ + 2e- ..... E0 = +0.7618V

    so it effectively lowers the iron half-reaction down to as low as -0.342V. The chlorine half-reaction can still overcome this so corrosion can still occur, but it is slower since the negative charge on the metal tends to keep the iron ions nearby increasing their concentration. These may get oxidized to ferric ions and form an iron oxide layer, but this too will tend to stay attracted to the metal being somewhat protective. The same principle holds with copper corrosion. With stainless steel, the corrosion is inhibited by a chromium oxide passivity layer, but that layer formation gets interfered with by higher chloride ion levels (such as happens somewhat more in SWG pools), but the negative charge on the metal allows for the exposed iron to not corrode as quickly.

    By the way, one can accomplish the same cathodic protection effect by using a power source instead of a zinc anode. Connecting the negative terminal of the power source to the bonding wire and connecting the positive terminal to a sacrificial wire to ground will also supply protection (this grounding wire and entry into the ground, however, will tend to corrode, just as a zinc anode would).
    16,000 gallon outdoor in-ground 16'x32' plaster pool; Pentair Intelliflo VF pump; Pentair IntelliTouch i9+3s control system; Jandy CL-340 square foot cartridge filter
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    Re: Adding salt-corrosion?

    So, in a nutshell, I could get a zinc rod a couple feet long and hammer it into the ground by the pump house. Then I would connect it to the bonding wire that runs to the pumps and that should provide some protection for the pool equipment. Sound like a good plan?
    12,800 gallon IG plaster kidney-shaped pool, waterslide, 800 gallon spa.
    1HP 2 speed Sta-Rite pool pump, 1.5 HP Sta-Rite spa jet pump. 2 skimmers, 1 main drain
    Purex-Triton TR-60 325 lb.sand filter. 2" Plumbing, Intex SWCG, TF-100 test kit.
    Link to pics of my pool! http://www.troublefreepool.com/my-oasis-t26558.html

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    Re: Adding salt-corrosion?

    Quote Originally Posted by guamguy
    So, in a nutshell, I could get a zinc rod a couple feet long and hammer it into the ground by the pump house. Then I would connect it to the bonding wire that runs to the pumps and that should provide some protection for the pool equipment. Sound like a good plan?
    Yes, that should work assuming you do not have any breaks in your bonding wire and assuming the ground has relatively moist soil (you need some level of conduction to ground for the zinc to sacrificially corrode).
    16,000 gallon outdoor in-ground 16'x32' plaster pool; Pentair Intelliflo VF pump; Pentair IntelliTouch i9+3s control system; Jandy CL-340 square foot cartridge filter
    12 Fafco solar panels; Purex Triton PowerMax 250 natural gas heater (200,000 BTU/hr output); automatic electric pool safety cover; 4-wheel pressure-side "The Pool Cleaner"

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    Re: Adding salt-corrosion?

    Also, what type of test should I use to determine the salt level? The strips or a drop-based kit? I know the salt level isn't critical, since I'm not using a SWG, just for improved water feel.
    12,800 gallon IG plaster kidney-shaped pool, waterslide, 800 gallon spa.
    1HP 2 speed Sta-Rite pool pump, 1.5 HP Sta-Rite spa jet pump. 2 skimmers, 1 main drain
    Purex-Triton TR-60 325 lb.sand filter. 2" Plumbing, Intex SWCG, TF-100 test kit.
    Link to pics of my pool! http://www.troublefreepool.com/my-oasis-t26558.html

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    Re: Adding salt-corrosion?

    The salt strips are less expensive and easier to use, the drop test is a little more reliable. In your situation either one would be fine.
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    guamguy's Avatar
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    Re: Adding salt-corrosion?

    Sounds good, think I'll give the strips a try to see what the salt level is before I start adding more.
    12,800 gallon IG plaster kidney-shaped pool, waterslide, 800 gallon spa.
    1HP 2 speed Sta-Rite pool pump, 1.5 HP Sta-Rite spa jet pump. 2 skimmers, 1 main drain
    Purex-Triton TR-60 325 lb.sand filter. 2" Plumbing, Intex SWCG, TF-100 test kit.
    Link to pics of my pool! http://www.troublefreepool.com/my-oasis-t26558.html

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