Chemistry Questions (TDS, CSI, heater)

[crek31]

So I have a long saga this season of not having a reliable pool heater. It works intermittently since start up in early June. Warranty repair person has been here twice and twice said all is well without really doing anything. That long sad story can be found here:
troubleshoot-a-mastertemp-t62022.html

My question here is to see if my chemistry could have caused a problem. They are coming out tomorrow to clean out the heat exchanger. They have not talked to me about why they think that is the issue but did email me that is what they are doing tomorrow. I want your input to see if I could have messed up the chemistry so bad as to ruin the heat exchanger after only one season of use, plus about a month this season -- that would be about 90 days total. I drain and re-fill each season, so I start with completely new water each season. Here are current numbers. Keep in mind I have only been full for a month, so although I am trying to get my TA down, it takes time. I add muriatic acid every time I get to 7.8 and go down to 7.2. Sometimes I even add at 7.5 to go down. My pH has never been below 7.2 or above 7.8. I test at least once per day and often in both the morning and evening.

Current numbers:
CYA: 20 or slightly higher
FC: 4
CC: 0
pH: 7.5
TA: 170
CH: 210
Temp: 81
Salt: about 700

Pentair's manual says if I don't stay in their parameters I will void the warranty. No one has suggested that is a problem in my repair story thus far, but my understanding is if they say the heat exchanger needs to be cleaned they are likely to blame the water chemistry.

Per Pentair the parameter are:
No mention of CYA in manual
FC: 1-5 (ideal 2-4)
CC: 0-.2 (ideal 0)
pH: 7.2 - 7.8 (ideal 7.4-7.6)
TA: 60-180 (ideal 80-100)
CH: 150-500-1,000 (ideal 200-400)
Total Dissolved Solids: max 1,500

Questions:

1. Pool Calculator shows my CSI at .12 -- there is no mention of that in the Pentair manual, but seems like to get that number in range per Pool Calc I need to add more salt. Should I? Does water with this CSI pose a risk to the heat exchanger or heater in general?

2. I don't see how to figure TDS in the Pool Calculator, nor did I see it in Pool School articles that seemed likely to discuss it (ABCs, Recommended Levels). Anyone know an easy way to calculate this, or is it a separate test I need to run?

 

[BoDarville]

1. Pool Calculator shows my CSI at .12 -- there is no mention of that in the Pentair manual, but seems like to get that number in range per Pool Calc I need to add more salt. Should I? Does water with this CSI pose a risk to the heat exchanger or heater in general?

A CSI of 0.12 is considered balanced. Wouldn't mess with your chemistry.

2. I don't see how to figure TDS in the Pool Calculator, nor did I see it in Pool School articles that seemed likely to discuss it (ABCs, Recommended Levels). Anyone know an easy way to calculate this, or is it a separate test I need to run?

There is a very good reason for this...TDS is a meaningless number. TDS stands for Total Dissolved Solids and consists of several components (salt, CYA, CH, and others.). A consolidated TDS number tells you nothing. For example, a TDS of 1,000 ppm could consist of Salt at 650, CH of 300, and CYA of 50. That combination of numbers is fine for a manually chlorinated pool. Another manually chlorinated pool could test at 1,000 ppm of TDS and be made up of Salt at 700, CYA of 150, and CH of 150. That set of numbers is problematic mainly due to the high CYA. The CH of 150 is fine for a vinyl lined pool, but too low for a plaster pool.

The conclusion: Both pools have TDS @ 1,000 ppm. The first pool is fine while the second will have problems due to CYA. However, the difference between these two pools is not distinguishable from the consolidated TDS number - it considers both pools to be the same. However, we know otherwise. You need to know the amounts of the individual components that make up the TDS.

 

[JasonLion]

1) No, CSI at 0.12 is fine. There is a bit more risk when PH is 7.8 and the water inside the heater is 90, but even that shouldn't be a real problem unless the TA started noticeably higher.
2) That is because TDS is completely irrelevant (aside from their warranty).

Nothing you mentioned will prevent them from claiming that the numbers were out of range at some point. Proving otherwise is difficult, something that they tend to take advantage of. Besides, if there is calcium scaling in the heat exchanger it more or less proves that your numbers were out of the ranges you mentioned at some point.

Better for you is if there is some obvious manufacturing defect when the heat exchanger is removed for cleaning.

 

[crek31]

Thanks. And yes, i am so bad at math (and quite distracted this week) that I really did think ."twelve" was higher than .6. Oops, thanks for your answers.