Low CSI

[Dabby]

I just tested the pool and all the results fall within the recommended levels. However, according to the pool calculator, the CSI is low, -0.74. Here are the results of the tests:

FC 10
CC 0
pH 7.5
TA 70
CH 280
CYA 70

Is everything ok, or do I need to do something to raise the CSI? What would be the best solution?

Thanks.

 

[susa]

Is free chlorine really 10 ?

CSI will get closer to zero with slight rise in pH.

 

[257WbyMag]

I don't see your water temp on there. Since you are close to me, I am going to assume that your water temp is close to mine and give you a value of 58 degrees. By plugging your numbers into the pool calculator and guessing that your water temp is 58 degrees, I get a CSI of -0.44 which is ok. Not sure how you are getting -0.74.

Anyway, the easiest way for you to bring your CSI up is for you to let your pH come up to 7.7 or 7.8.

 

[Dabby]

The FC is 10. It is actually starting to come down. It had been rising even though I was reducing the generator, but I wasn't doing it in large enough increments. I was afraid of going too far. It is now off until the chlorine level comes down.

The water temp at the time I did the tests was 50. You must live in the tropical area of DFW. If you still come up with a different value, please let me know.

I was trying to keep the pH down because it rises so quickly (new plaster pool). Maybe I should let it rise a little and keep a closer eye on it.

 

[257WbyMag]

Even with the water temp of 50 degrees, I'm still only getting -0.52 on the CSI. Still technically ok but getting close to corrosion potential.

Because you have new plaster, you are in a spot where you are going to have to keep a closer eye on things than you might normally need to. I would let the pH come up and try to keep it around 7.7 or 7.8. This dramatically affects your CSI. Of course, you could do other things such as raise your CH or bring your TA up, but I think that simply letting the pH rise would be the best thing to do.

 

[duraleigh]

Maybe I should let it rise a little and keep a closer eye on it

I wouldn't.

I am not a big fan of CSI as, IMO, it adds one other thing to "worry" about and, if your numbers are within the parameters suggested on the forum, calcium scaling will not be an issue.

You are within those numbers and scaling will not be an issue. Letting your pH get at the upper limits of suggested, especially when you have a tendency for pH to rise anyway would seem to me to make your pool management more difficult. I would leave pH alone, and have confidence that your numbers are all quite good and you will have no issues.

How does your water look?

 

[susa]

> keep the pH down because it rises so quickly (new plaster pool).

hope this is not literally new plaster as I was told to hold off running the SWCG until at a minimum 30 days from build/resurface and TFP recommendation was to hold off 60 days before adding salt.

in my case, despite balmy 22 C days, it gets down to 11 C at night so plan on maintaining pool with just liquid until winter is over and SWCG can "sleep".

 

[Dabby]

I just figured out why we are getting different CSI values. I did not mention the salt level is 3100.

It is not ""brand" new plaster, just "new" new. It's been about two months since we added salt.

I was worried about was the phrase from the pool calculator: "A low saturation index means the water is likely to dissolve calcite out of plaster, pebble, tile, stone, and concrete surfaces (and perhaps fiberglass) which will eventually cause damage."

I don't know how sensitive or accurate these things are. -.74 seems pretty close to -.6, so I'm not sure if I should worry about it or not.

 

[PaulR]

I was worried about was the phrase from the pool calculator: "A low saturation index means the water is likely to dissolve calcite out of plaster, pebble, tile, stone, and concrete surfaces (and perhaps fiberglass) which will eventually cause damage."

CSI is a measure of long-term risk more than a knife-edge death-or-glory metric. It's about the last thing to worry about chemistry-wise, and like duraleigh, some people don't worry about it at all.

Given that this is a relatively new pool and the plaster is still doing its new-pool thing, I'm reluctant to suggest bringing the CH up any. It should not be harmful to run the pH more toward the higher end of the normal range (7.7-7.8) if it makes you feel better, although as you say you'd have to monitor it more closely.

If you're still in this situation when the pool is a year old, then it might be time to think about raising CH a bit.
--paulr

 

[Dabby]

Ok, now I understand. CSI is more of a "trend" value to keep an eye as opposed to an immediate indication of a problem. Correct?