Question about calcium when you have a heater

[Tcap]

Hello,

I have a 33,000 gal. IG vinyl pool with SWG. It was install at the end of season last year so this is our first opening. So far, so good. We have a propane heater on the pool - young kids and it helps take the chill off after cold nights up here in NH - Anyway, I was told that I need calcium in the water to maintain and extend the life of the heater. It's a Hayward H400. I know my calcium is at 0 right now and I have hesitated listening to my pool people as I have read so many times that a vinyl pool does not need calcium. OK, so my pool may not need the calcium, but does my heater? Should I keep a certain level of calcium in the water for the heater? What would be the logic to adding calcium with the heater?

By the way, I have been using the three B's system and the pool is in great shape!

Thanks!
Tracy

[mwsmith2]

Yes, with a heater you need Ca. The reason why was on the old board, but I forget right off hand. I think the best support for it is the SI calcs...it's easy to go corrosive without Ca in the water. From the quickie checks I did before, you'll only need about 150 ppm to keep everything happy.

Maybe Ben can remind me of why this is! :D

(or maybe he can tell me why i'm wrong!)

Michael

[mas985]

Michael, you are correct. Ca is needed for the saturation index. Water temp, PH, alkalinity, calcium hardness and total dissolved solids are all used in determining the saturation index. If the SI is too low, any metal in the pool will start to dissolve. Heaters are especially vulnerable due to the metal content in the heat exchanger.

Tracy,

If you can post the PH, Alk, Temp, Ca and salt level, I can give you the SI. To learn about it yourself, Google: "Langelier saturation index" for more information.

Also, here is an online calculator: http://www.advancedh2o.com/technical/calculations_and_tables/langlier.html

[Tcap]

Tracy,

If you can post the PH, Alk, Temp, Ca and salt level, I can give you the SI. To learn about it yourself, Google: "Langelier saturation index" for more information.
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Hi, Here are my numbers. I was up around 10 for Cl but now everything is clear and the numbers were maintaining PM to AM so I'm starting to let it come down. Anyway:
Cl: 5
PH: 7.8
CYA: 30
Alk: 110
Temp: varies in this climate but 55 right now
Ca: none showing up
Salt level: 100 - just starting to add salt now that everything is stabalizing so this number is in flux.

Question about the LSI - if some of it is based on Temp. and that's so variable in an outdoor pool - how is it possible to keep the ideal saturation? It's 55 in the pool now and although we are not using the heater yet, it would be 80 or so running through the heater. Doesn't that just blow that variable away? Or is my logic off?

One more question: the ranges I'm seeing on test charts is 200 to 400 for pools. Should I be in the range or is that what is recomended for non-vinyl pools? Michael, you said 150 is fine. May I ask why 150 and not 200? I don't want to damage my heater, but I also don't want to waste money adding more calcium than I need.

Thanks for your help! It's been such an education. I feel like the mad scientist lately!!

-Tracy

[mas985]

Because your Ca is 0, your SI is about -2.3, which is very corrosive. If you can get Ca to 200 and salt level to 2800 and a PH of 7.9 your SI will be zero or optimum.

Actually, water temperature in an outdoor pool is fairly seasonal so it is not that difficult to keep SI in check. Also, temperature has a minor affect on SI. So using the balanced example above, you need a PH of 7.9 for a temp of 55 degrees and a PH of 7.7 for a temp of 80 degrees. As Alk or Ca rise, your optimum PH drops. Also, chlorine works better for PH < 8 so you may want to target for a PH lower than that.

It is ok to let the SI swing between +- .5 and even better to keep it +- .2. Since PH is linear with SI, this means that you can have a +- .2 swing in PH to be near optimum so it should not be too hard to keep it in check.