How important is it to familiarize w/ CSI?

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minimonster17

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Jul 22, 2013
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Realistically, how important is it for the owner of a newly constructed gunite pool to be familiar with the calcite saturation index? I understand the basic scientific concept that having an inadequate concentration of CH in the water opens the possibility for the water's craving to dissolve calcium carbonate, which in turn would result in etching of the pool walls.

I performed a thread search, which yielded technical posts mostly by chemgeek that contained equations which would be fairly difficult to perform calculations with manually. I have not dealt with such in-depth manual calculations since being in my senior year of high school.

I suppose what I am asking if doing the basic tests on a regular basis myself, particularly watching ph and ch and using the pool calculator as necessary would suffice, or do I need to further familiarize myself with the technicalities of the CSI in order to prolong the life of a plaster job as long as possible.

I haven't even built my pool yet, but am currently trying to learn as much as I can before taking the plunge, so to speak.

The water I will be using to fill my future pool comes from my house's well. The plaster surface of the pool will be a product similar to diamond-brite.
 
Maintaining a CSI at or very near zero is very important. Let it get too high and your pool will be covered with heavy scale. Let it get too low and it will disolve the grout and damage the surface of the pool. With the online Pool Calculator you just do your regular tests, record the numbers and it calculates your CSI for you. It really makes it simple to watch and control your CSI.
 
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It's more important for the CSI to be near zero or slightly above zero when the plaster is new. After it is cured, if the plaster is of high quality, some variations in the CSI will not degrade it or not do so quickly, but over years it's harder to say what the effects will be though if plaster does dissolve, this may be noticed by a rising CH (or not dropping as much as expected by dilution). Low pH with a negative CSI is the most detrimental to cured plaster.
 
For newbies reading this thread, there are many of us on the forum that never use the CSI. Maintaining pH, CH and TA all within the suggested guidelines puts your CSI in a satisfactory range to begin with so it becomes somewhat superfluous.

I see value in it during a new plaster startup perhaps but aside from that circumstance, maintaining those three parameters will be sufficient.
 
I think the gray area is what "near zero" means. I have a new plaster surface (2 months) and my csi varies no more than +/- 0.2. I do have to add about a quart of chlorine and 12 oz of acid a day.

Regards
Michael
 
The great majority of pool owners can completely ignore CSI. As long as you maintain your levels within our recommended ranges your CSI will be taken care of. The main time you need to worry about CSI is when your TA or CH levels are unavoidably high, for example when your fill water is high in either TA or CH or both. Then you need to start adjusting your other levels to keep CSI from getting out of bounds.
 
Not picking on Chief, but using this as an example.

chiefwej said:
Maintaining a CSI at or very near zero is very important. Let it get too high and your pool will be covered with heavy scale. Let it get too low and it will disolve the grout and damage the surface of the pool....
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I I were a newbie reading this I would be in full blown panic! Since my CH is zero the CSI for my pool is "-INF"! What I know that most newbies don't, and isn't quantified in the above statement, is that low CSI means nothing in a vinyl pool.

I think that concentrating on having the chems that are pertinent to the type of pool balanced is way more important than focusing on a single calculation. I agree that there are probably special circumstances, but those should be handled on a case by case basis. We shouldn't try to cover those with a blanket statement.
 
The Calcite Saturation Index is about saturating the water with calcium carbonate. This is for pools where the water is exposed to surfaces that contain calcium carbonate such as pool plaster and grout in between tile. If you have a vinyl pool, then there is no need for such saturation so having a zero or low Calcium Hardness (CH) does not matter (see this thread for technical info about this). For fiberglass, the use of calcium may prevent some cobalt leaching or staining but the amount needed for this purpose is not known definitively.

Some other threads about the CSI are the following:

Langelier and Calcite Saturation Indices (LSI and CSI)
Calcite Saturation vs. Calcium Level for Plaster Protection
Is the Saturation Index always Reliable?

Since experiments with plaster coupons showed a slow degradation of plaster when the saturation index was between -0.6 and -1.0, then yes a range of -0.3 to +0.3 would be considered to be near-zero. It was also shown (in this post) that the CSI itself is what matters and not a single low water parameter (in particular, CH or TA) in terms of making the water aggressive towards plaster. On the high side, we normally don't see scaling until the saturation index is +0.7 or higher in pools and usually +1.0 or higher but saltwater chlorine generators get noticeably more scaling in the SWG cell even with a CSI near zero because of the higher pH at the hydrogen gas generation plate, so for SWG pools a somewhat negative CSI is often used along with 50 ppm Borates that act as a pH buffer that cuts the amount of pH rise near the plate in half. In hot spas, I've seen reports where scaling occurs (starting in the gas heater heat exchanger where the temperature is around 30ºF hotter) when the CSI is above around +0.3 so the hotter temperatures may accelerate this effect.

Note that at the Recommended Levels for a plaster pool with the lowest pH, TA, CH, highest CYA and low temperature (77ºF), the "with Bleach" CSI is -0.29 (-0.44 if TDS is 2000) while the "with SWG" (and TDS of 3000 ppm) CSI is -0.70. With the highest pH, TA, CH, lowest CYA, and highest temperature (90ºF), the "with Bleach" CSI is +0.40 while the "with SWG" CSI is +0.05. I've brought up before that perhaps the CH recommendation for the "with SWG" should be a little higher (350-450) though we do want the CSI to be somewhat lower for SWG pools to prevent scaling in the SWG cell and that would still be the case even at this higher CH level. The higher CH would compensate for the lower TA recommendation and the higher TDS in SWG pools.
 

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To Bama Rambler: The sole reason I posted this in the Deep End section was because I was aware of the implications of something as in-depth as the CSI. This thread obviously doesn't belong in BBB or Chem 201, and I posted here as such, knowing that there always a solid, definitive answer when it comes to this stuff.

I was also previously aware of the fact that the plaster doesn't reach full cure strength up until a year after pool is started. I guess what I'm wanting to know, that when I construct my pool and start it up, should I calculate and maintain a certain level of CSI, at least during the first year, or only use the Pool Calculator? I thought I read on here that the pool calculator has the parameters/correction factors for CSI built into it, but I am unsure of that?

I failed to mention in my first post that the pool will be SWG. What is the somewhat negative CSI you are referring to in such an application, Chem Geek? I had also planned on adding 50 ppm borates as well after the SWG is turned on.
 
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CSI is very important to me because of my high CH. My fill water is 150 CH so I'm always fighting rising CH. It's currently at 650. I added borates and I adjust pH and TA such that I always have a near zero to slightly negative CSI. My choice is to frequenly drain water or manage pH and TA to keep the CSI down. I prefer not to drain water all of the time. My fill water is high in TA (220) so refilling requires a lot of MA to reduce it and I also would have to top up the borates (needing more MA) and CYA. I love it when it rains.
 
I apologize, if I sounded like its an issue that every newbie should be panicked about. But, at least for me it's of real concern. I have a SWG, my fill water has a TA near 300 and high CH. the evaporation rate here in the desert is extreme. I just went through a season managing a CH over 1,000. So, monitoring the CSI has been a real issue, and with my limitations there was little margin for error.

Now, I've got 50 ppm borates in the pool, brought my TA down around 70, and did a drain and refill to get the CH in the 250 range. So now things are getting back to normal.

I agree that for most people you can just keep your other numbers within standards and CSI should remain in a safe range. But once you are forced to deal with situations and limitations other than he acceptable standards it becomes very important.
 
minimonster17 said:
The water I will be using to fill my future pool comes from my house's well.
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Do you know the chemistry of your well water, especially TA, calcium hardness, sulfates, and metals such as iron, copper and manganese?

Do you have another source of water?
 
I'll see if I can find the results of the water test that was done during the loan process of when we bought our house. I don't have a test kit yet to perform testing on the water myself. I have no other source of water available offhand, there is no municipal supply out here. I'll let you guys know what I find out.

edit: Water testing report does not include amounts of trace metals/minerals present. All it says is no chlorine found, and water suitable for drinkability. I'll have to test the water myself for TA and CH when I get the test kit. How would I perform tests for metals? I don't believe the test kit we sell on here includes those tests?
 
The tests for metals are expensive and you use them very infrequently so usually you go to a pool store for those tests and cross your fingers that they do the tests correctly. [EDIT] See James post following mine -- that's much more relevant for testing well water. [END-EDIT]
 
A water treatment place should be able to test for metals. If you want a state certified laboratory to test your water, you can contact your state's certification officer for a list.

http://water.epa.gov/scitech/drinkingwa ... cation.cfm

Your state might have a Residential Well Program, such as this one in South Carolina.

https://www.scdhec.gov/environment/wate ... esting.htm

Your local Health Department should be able to help you with information regarding well water testing programs and certified labs.

It would probably be worthwhile taking a sample by a pool store, or two, to see what they get for TA, Calcium Hardness, iron, copper and manganese.
 
Not to ask a stupid question, but how large of a water sample would I take to the pool store? I have never even set foot in a pool store before, and don't foresee myself doing so much thanks to the cumulative knowledge of this board.

I don't have any alternative to using my well water, as I really don't want to have water trucked in for the pool's start-up.
 

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