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Hydronic hardness testing and treating.

icy78icy78 Posts: 251Member
What do you guys use to check the hardness of the water in the boiler system. I do have a PCSTestr 35 meter and that will show pH, conductivity ,TDS ,and temperature. I think that was all. But I'm wondering what's the best way to determine the hardness of the water?
Also, from the reading that I've done, it seems a fairly complicated process to determine what additives would need to be used to Rectify say high TDS. I just pulled a water sample and it shows a TDS of 320 and the conductivity of about 450.. I did call the owner and found out that it's probably fed with softened water and definitely has had leaks, so water has been added. This system probably holds 2- 300 gallons maybe more and having read a number of threads on this site about it I see where @Hotrod says that it's a fairly complicated business knowing how to treat the water. So I guess one of my questions would be do you just add a Rhomar or Sentinel 100 in there after Flushing the system, or is it a good idea to bring in a water treatment company and get a relationship with them?
I have read the caleffi hydronix 18 water treatment manual. One of our Engineers is starting to use some of those products so I have hopes that we will be progressing! LOL


  • icy78icy78 Posts: 251Member
    Any input guys?
    I missed this formula before..., so will the fomula gpg=TDS÷17.1 give hardness?
    If so, and the TDS is 330. That's a hardness of approx 19. Is that possible? Seems really high. I don't know if any additives have been added.
    I'm guessing the formula is shown incorrectly in idronics 18. It shows
    1GPG X 17.1 = 1 ppm
    Prob should be =17.1 ppm
  • ChasManChasMan Posts: 459Member
    FWIW, I use the Hach Labs hardness kit. I found even moderately hard water in a closed loop system will scale my boilers so I treat it with a sodium ion exchanger just normal water softener.
  • Jamie HallJamie Hall Posts: 10,548Member
    The Hach kit is fine for what we are usually doing with boilers. That said... I'd be very wary about using softened water for a boiler. Why? Yes, it does reduce the hardness -- but ion exchange softened water introduces sodium and chloride instead, and reduces the buffering capacity of the water at the same time. This is an excellent way to ensure that you will get corrosion and leaks in the system.

    Much better, if the water is hard enough to cause a scale problem, is to use distilled or reverse osmosis treated water, and add a buffering compound to hold the pH around 7 or 8, and an oxygen scavenger. Don't go overboard on the chemicals -- the correct amount is important, and too much is probably worse than too little.

    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • hot_rodhot_rod Posts: 11,624Member
    This type of test kit is the way to go. You can buy test strips at most any box store, the drop test is easier to read and more accurate I feel.

    TDS and softness are not exactly the same. the hardness test kits are looking for the scaling minerals, TDS looks at all the ions in the water. It is not a direct conversion from one to the other.

    Often when you soften water the TDS goes up, not down. Best is demineralized water or RO. It's tough to find large quantities of true distilled water.

    Read up about the difference between ion exchange softening or demineralized water below.

    Or collect some rain water, it is naturally soft.

    I would add a hydronic conditioner to pure DI or RO water to buffer ph, add o2 scavengers and film providers.

    Most boiler manufacturers want hardness under 10 gpg x 17.1 = ppm.

    The TDS that is acceptable varies from manufacturer to manufacturer, if they even give a spec.

    TDS, hardness and Ph are good numbers to know. Testers for all 3 are fairly inexpensive.

    Of course cleaning the system with a hydronic cleaner is a good step also.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
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