CH and CSI- high CH but CSI negative?

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Kidneydoc

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Aug 29, 2013
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Vero Beach, FL
FC=5
Ph=7.5
TA=50
CH=650
CYA=90
Salt=3000
Borate=40
SWG pool
13,500 gallons, plaster pool
Temp=80 (Florida)

I was concerned about my CH going up (now 650). I read various posts about watching the CSI. With the Pool Calculator, my CSI is like -0.56. So it appears to be at risk for leaching calcium from the plaster. However, if I start plugging in numbers in the calculator, I would have to get the CH up to 1500 to get the CSI out of the "danger" zone to -0.2.

My pool has been fine for 2 years...no scale, no SWG problems. So, do I worry about leaving the CH "too low" at 650? (...but it seems like this is a a high CH according to the suggested levels)....or do I need to take the CH up even more?

Thanks for any input!
 
The formula to determine CSI takes several things into account, not just CH. Play with pH, TA & temperature and you will see changes. If you keep your numbers within our recommendations you will generally not have a problem with CSI.
 
If you keep your numbers within our recommendations you will generally not have a problem with CSI.
Click to expand...
I agree wholeheartedly. In fact, if you keep your numbers within our recommendations you will virtually NEVER have a problem with any scaling issues in your pool.
 
Thank you for input, but I am still confused. The Pool Calculator using the suggested levels of CH of 300 will actually give me a CSI of -0.9.

Have been doing TFP method for many years, so I understand the basics. However, I have not not had high CH until recently. So, not sure what the "recommendations" are in terms of CH.

As per my first post, I am keeping the FC=5, CYA=90, Salt= 3000, TA=50, BA=40 (or so)....but the CSI will be very negative until i plug in a CH of almost 1500 on the pool calculator. (..."at risk to plaster" per pool calculator at current level of -0.55)

So, this is my confusion....do I need to add Calcium to push my CH higher than my current 650 (...which currently gives me a CSI of -0.55 or so)?

thanks
 
.....in other words, if the "recommendations" are followed, the CSI is -0.81, which indicates risk for corrosion of plaster (...as it is more negative than -0.6).

This is what is confusing me. It seems the CH has to be very high (as above...around 1500) to get the CSI closer to 0.

Thanks!
 
As I said above, CH is not the only player in the CSI game. Your TA is lower than our recommendations. Just by bringing the TA up to 70 your CSI drops to 0.06 With TA of 70 and bringing the CH down to the high end of our recommendation (350) your CSI is -0.15

Recommendations for a Plaster SWG Pool

FC (See chart)
pH 7.5-7.8
TA 60-80
CH 250-350
CYA 70-80
 
Also, so things can be easier kept in context (like you live out west in a high CH area) can you do us a favor an add your city and state to your profile. This helps us deliver better answers to questions asked.

Additionally, if you would add the following information to your signature


  • The size of your pool in gallons
  • If your pool is an AG (above ground) or IG (in ground)
  • If it's IG, tell us if it's vinyl, plaster/pebble, or fiberglass
  • The type of filter you have (sand, DE, cartridge) and, if you know, the brand and model of the filter.
  • If you know, please tell us the brand and model of the pump, and mention if is it a two speed or variable speed pump.
  • Date of pool build/install, particularly important if less then a year old.
  • What kind/model of water test kit you are using
  • Other significant accessories or options, such as a spa , SWG, or cleaner
Thanks
 
PH is probably the biggest factor with the CSI. Keep the PH around 7.8 and that should resolve your issues. Warmer water temperature can also help.

Your TA level is on the low side but should be fine since you are using borates. You could raise the TA to 60-80 which will also raise the CSI.

Plenty of people deal with CH levels much higher than yours...play with the calculator and see what works for you. The CH level doesn't really have as big of an impact on the CSI as you would think. Raising the PH and TA will give you the biggest gains in the right direction.
 
tim5055 said:
As I said above, CH is not the only player in the CSI game. Your TA is lower than our recommendations. Just by bringing the TA up to 70 your CSI drops to 0.06 With TA of 70 and bringing the CH down to the high end of our recommendation (350) your CSI is -0.15

Recommendations for a Plaster SWG Pool

FC (See chart)
pH 7.5-7.8
TA 60-80
CH 250-350
CYA 70-80
Click to expand...

CSI also takes salt, temp and borates into account. With the low end of the recommended levels you end up with a CSI of -0.71:

PH 7.5
TA 60
CH 250
CYA 70
Salt 3600
Borate 50

It takes a PH of 7.8 to get the number up to -0.56, which is at the top end of the recommended level and very near -0.6.

His higher CH is actually beneficial for keeping his CSI up.
 

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OK...thanks....Chem Geek always to the rescue!

I will push my TA up some and not worry too much about the negative CSI. At some point, I will drain some water and get the CH down to 300 ish. My fill water is not too bad (about CH of 70), so it would not be too hard to do a 1/2 pool drain / fill at some point.

Thanks again!
 
A negative CSI is actually what you want in a SWG pool. Your CH level is not a problem where it is now so no need to drain unless you are having other issues.

How did your CH get that high if your fill is so low? Is the pool really old?
 
Pool is from 2006.

I moved into this house in 2013, and I do not have any history on any drain/fills and I have not drained pool since I have owned it.

I checked the CH over a year ago, and I think it was 450 or so. I did not bother rechecking until recently, and never thought much about the CH until now.
 
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