Corroded Water Heater

Chad628

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LifeTime Supporter
Jul 30, 2013
99
San Francisco Bay Area
#1
Hello all,

PH 7.5
TA 50
Borrates 50
CH 130
CYA 30
Chlorine 4

I recently had to replace a corroded water heater in my hot tub. I just re read the sticky about how to use chlorine in your hot tub and noted in the paragraph about PH that it mentions if your CH is too low it can cause your heater to corrode. I try to maintain the target numbers for water chemistry recommended in that sticky yet I had a corroded heater. How do I know what is too low for my CH? Does the calcium saturation index indicate when corrosive conditions exist in my water chemistry? What is a good range for CSI in a hot tub?

Thank you very much.
 

Patrick_B

TFP Expert
LifeTime Supporter
Jun 7, 2011
14,999
Midland TX
#2
CSI corrosion applies to plaster not metallurgy. The lack of CH in water would not have any comparable effect compared to that of pH, which would be by far the biggest driver in the corrosion of a metal pool heater. Very high Chlorine could also be a factor in metal corrosion, but I would put my money primarily on low pH here. Low CH, unless it was very, very low would be a minimal contributor. PS: Even then, other water balance factors would have to be in play that are seldom if ever present in pool water.
 
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Chad628

Chad628

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Jul 30, 2013
99
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#3
Patrick I use the dichlor then bleach method as recommended in the "How to use chlorine in your hot tub" sticky. My PH tends to rise due to the use of the hot tub jets and I don't overshoot with my addition of muriatic acid to cause the PH to be too low. I was surprised when the hot tub tech mentioned that my hot tub chemistry was the probable cause of the corroded heater because I religiously follow the advice of the TFP web site for maintaining my hot tub chemistry. Is the information in the "How to use chlorine in your hot tub" incorrect with the following quote:

"However, and this is important, just because you have a pH of 7.5, doesn't mean your water is balanced. If your CH is too low, you could be corroding your hot tub heater. If your TA is too high, you could be forming scale in your tub. Both of which will reduce your sanitizer effectiveness. So it is very important to have balanced water along with an ideal pH."
 

pooldv

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Aug 10, 2012
24,993
DFW, TX
#4
We need to update that. What they are referring to is low CSI which can cause problems with plaster but not metal. Low pH, below 7.0, along is all that can hurt copper. And if the heater is titanium then even that won't hurt. Sounds to me like water chemistry did not contribute to your heater failure.
 

JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
14,693
Tucson, AZ
#7
Sometimes hot tub manufacturers use the cheaper Incoloy heater elements as opposed to titanium (sadly, retail price difference is like $20 so why even consider Incoloy is beyond me). Incoloy has decent corrosion resistance but titanium will last 2.5 to 3 times longer.

Basically the constant heat cycling along with a chloride rich environment is going to kill an Incoloy heater. Titanium is much more resistant to chloride attack. All electric heaters die eventually, there's no way around it. There's no magic chemistry that will not corrode a heater.


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JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
14,693
Tucson, AZ
#8
Also, I would recommend a slightly higher calcium hardness, like 250ppm. It's not that hard to raise it up and even with 250-300ppm CH, it's very easy to maintain a balanced CSI using pH and TA as your levers.


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Chad628

Chad628

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Jul 30, 2013
99
San Francisco Bay Area
#9
Any update to the "How to use chlorine in your hot tub" sticky that would help clarify proper hot tub chemistry would be greatly appreciated. I know I have relied on that sticky extensively for maintaining my hot tub and I assume many others on this web site do as well. JoyfulNoise mentioned increasing my calcium levels in the 250 - 300 ppm range. Is that better advice than the recommended 130 - 150 ppm range as suggested in the sticky? Thank you for all the advice.
 

JoyfulNoise

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Platinum Supporter
May 23, 2015
14,693
Tucson, AZ
#10
I would say one reason for my recommendation is that, where I live, it would be impossible to fill a hot tub with water and have the CH that low. My water is already 180-200ppm CH. And since CSI can easily be adjusted using pH and TA, there's no reason for CH to be that low. I think the person that wrote that sticky lived somewhere where water is naturally soft.


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pooldv

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Aug 10, 2012
24,993
DFW, TX
#12
I agree, it is a great sticky and I have used it to maintain my tub for years. I have made some updates already and opened a discussion behind the scenes on the merits of increasing our recommended CH level to 250. Traditionally, we have only recommended CH of 130 to 150 in tubs to reduce foaming if it occurs, otherwise it is typically ignored. CSI below scaling level (+0.6) is all we have been concerned with because standalone hot tubs aren't plaster, they are acrylic, fiberglass or plastic. So, negative CSI is not an issue. Just as it isn't issue in vinyl or fiberglass pools, because there is no plaster to leach CH into the water and etch the finish.

It certainly will not hurt anything to increase CH to 250 in your tub. There is no downside, other than time and money to add it. From what I've seen you have done well managing the water chemistry in your tub. I don't think you contributed to your heater failure. And I'm not sure that increasing your CH to 250 would have prevented your heater failure or extended it's life significantly.

Thanks for the feedback and discussion.
 

JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
14,693
Tucson, AZ
#13
The key is not to let the CSI go above 0.6 when the tub is hot. So find a CH, pH and TA that achieves that while trying to maintain a CH near 200ppm. That will jeep you in line with most manufacturer specs and avoid warranty issues and mean looks from spa "professionals".


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Chad628

Chad628

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Jul 30, 2013
99
San Francisco Bay Area
#17
There was scale on the heating elements and some rust and corrosion on the housing around the area of the temperature sensors. The repairman who replaced it said that it would possibly start to leak from the corrosion.