# Thread: Pool Math and CSI question

1. ## Pool Math and CSI question

Was reviewing the Pool Math calculator after seeing some comments on CSI numbers which is a term I am not very familiar with.
Current numbers:
FC: 6.5
CC: 0
CYA: 70
PH: 7.4
TA: 60
CH: 120

These numbers have been pretty steady over the last couple months with PH slowly rising to 7.8 and then I add a little MA to bring it back down usually targeting 7.4. Adding a little bleach each day. Normally a little over a gallon a week. Pool is new last Sept. and I have never had any issues, water has always been clear. I figured everything was good. Then I started reading some comments mentioning CSI.

Over to Pool Math and per these numbers with a 70 degree pool it gives a CSI number of -.87 which it says is dangerous to my plaster. I have mini-pebble stonescapes, so does this apply in the same manner? Playing with some numbers raising PH to 7.8 gets to -.51 which it says is borderline. Should I leave PH at 7.8? raise CH?

Any suggestions for how much concern I should have with this CSI number, or what I should be looking to change to adjust the CSI number as we head into a Texas summer?

2. ## Re: Pool Math and CSI question

You have a plaster pool. Plaster is what holds those pebbles in place. You don't want to start dissolving it. You'll start loosening pebbles when you brush.

Play with poolmath some more. When the water gets up to 80, CSI goes down. Lowering pH no lower than 7.6 when it rises will reduce CSI. Raising TA to 80 will make CSI go down. Raising CH to 250 will make it go down.

TA is easy... dump in some baking soda. One 4 lb box will fix that.
pH will naturally rise. Even easier.
CH can be increased by either buying Calcium Increaser or by switching to Cal-hypo to chlorinate for a while. A 25 lb bucket of 73% Cal-hypo will add 145 FC and 102 CH. The problem is that it will take you two or three months to use that much FC so it will take just as long to raise CH. So just adding the straight CH will probably be better.

Don't ignore Effects of Adding Chemicals down at the bottom of poolmath. It will crunch the numbers for you. Know that CH will slowly rise as you replenish water lost to evaporation, unless you fill it from softened water, so don't push it all the way to the upper limits. Leave some room.

3. ## Re: Pool Math and CSI question

Looking at your numbers the main one that concerns me is your CH level. I am going to assume you have a SWG thus increasing your CH levels to 350 will greatly help your CSI level. From there maintain your levels around the Pool School - Recommended Levels chart and all will be just fine.

4. ## Re: Pool Math and CSI question

Your CH is a bit too low for a plaster pool (strange, considering your location) so, if you're confident that CH value is correct, then I'd say you should add some CH increaser and get it up to at least 200-250ppm.

What is the CH if your fill water?

5. ## Re: Pool Math and CSI question

No help here - but following - CSI is confusing to me - so trying to learn . . .

6. ## Re: Pool Math and CSI question

The best way to worry about CSI is to simply forget it. As long as you're able to maintain the Pool School - Recommended Levels on your water you'll be just fine. It's only if you're not able to maintain these levels you'll need to worry about CSI. The OP here can greatly help themselves by increasing the CH and maintaining this level. If they can keep everything in line CSI can be crossed off of the list of things to worry about.

7. ## Re: Pool Math and CSI question

Thanks for information, that was my assumption as well that I could mostly keep levels and ignore CSI. FYI I have just a regular pool, no SWG. Being new I have been focusing on primarily on FC/CYA/PH.

Reviewing the docs, it looks like I must have been reading the CH on the vinyl pool (CH 0-350), not plaster (CH 250 - 350 ) My PB also mentioned a very wide range and I have assumed that 120 is okay. Looks like if I just raise that to 250-350 and leave PH at 7.6 or higher it gets me into a more reasonable range where I probably don't have to worry about CSI as you stated.

I have put baking soda in to raise TA, but when I do that it tend to drift back down pretty quickly (days) back to the 60 range where it seems to be stable, so I have been mostly leaving it there. I guess bringing that back up to the lower 70 range would also help.

Thanks for all the suggestions / help. I think this makes a bit more sense. Out of curiosity, how long does it take for an out of range CSI to cause problems? Is it days, weeks, or more of a long term situation?

8. ## Re: Pool Math and CSI question

Originally Posted by Sunbaby
No help here - but following - CSI is confusing to me - so trying to learn . . .
Easy-peasy Wendy....you like to cook, right? Have you ever made rock candy before?

To make rock candy, you heat water to a boil and add sugar (with a little bit of acid from lemon juice to break the sucrose down into fructose and glucose). You keep adding sugar until you get a pretty good sugar syrup boiling. Remove the solution from the heat, pour it off into a clean glass jar and dip a stick in it. Keep the glass jar covered and undisturbed in a cool part of the kitchen. Let the stick dry for a day. Put the stick back into the sugar solution and let it sit there for a few days.

What happens? Giant sugar crystals grow on the stick!

Now, take lollipop and put it in a glass container with hot water. And let it sit there.

What happens? The lollipop slowly dissolves into the water.

What you see there is saturation (or lack thereof) in action. When your pool water is unsaturated with calcium, it's like the lollipop in hot water, the calcium from your plaster will dissolve. When your pool water is over-saturated with calcium, it's like making rock candy, calcium (as calcium carbonate) will want to grow all over your pool surface. The CSI is nothing more than a measure of how over-saturated or under-saturated your water is with calcium carbonate. If your CSI is excessively positive, then there is a chance calcium scale will form under the right conditions. If your CSI is excessively negative, the water will dissolve calcium from any source it can find, eg, your plaster. Unlike rock candy which only depends on how much sugar you dissolve in water and what the temperature is, CSI also has to factor in pH and TA as well as some minor variations based on salt and borates.

9. ## Re: Pool Math and CSI question

OHMYGOSH!!! You should be a teacher - that made more sense then EVERYTHING else I have read! Thank you!

Originally Posted by JoyfulNoise
Easy-peasy Wendy....you like to cook, right? Have you ever made rock candy before?

To make rock candy, you heat water to a boil and add sugar (with a little bit of acid from lemon juice to break the sucrose down into fructose and glucose). You keep adding sugar until you get a pretty good sugar syrup boiling. Remove the solution from the heat, pour it off into a clean glass jar and dip a stick in it. Keep the glass jar covered and undisturbed in a cool part of the kitchen. Let the stick dry for a day. Put the stick back into the sugar solution and let it sit there for a few days.

What happens? Giant sugar crystals grow on the stick!

Now, take lollipop and put it in a glass container with hot water. And let it sit there.

What happens? The lollipop slowly dissolves into the water.

What you see there is saturation (or lack thereof) in action. When your pool water is unsaturated with calcium, it's like the lollipop in hot water, the calcium from your plaster will dissolve. When your pool water is over-saturated with calcium, it's like making rock candy, calcium (as calcium carbonate) will want to grow all over your pool surface. The CSI is nothing more than a measure of how over-saturated or under-saturated your water is with calcium carbonate. If your CSI is excessively positive, then there is a chance calcium scale will form under the right conditions. If your CSI is excessively negative, the water will dissolve calcium from any source it can find, eg, your plaster. Unlike rock candy which only depends on how much sugar you dissolve in water and what the temperature is, CSI also has to factor in pH and TA as well as some minor variations based on salt and borates.

10. ## Re: Pool Math and CSI question

Originally Posted by JoyfulNoise
Easy-peasy Wendy....you like to cook, right? Have you ever made rock candy before?

To make rock candy, you heat water to a boil and add sugar (with a little bit of acid from lemon juice to break the sucrose down into fructose and glucose). You keep adding sugar until you get a pretty good sugar syrup boiling. Remove the solution from the heat, pour it off into a clean glass jar and dip a stick in it. Keep the glass jar covered and undisturbed in a cool part of the kitchen. Let the stick dry for a day. Put the stick back into the sugar solution and let it sit there for a few days.

What happens? Giant sugar crystals grow on the stick!

Now, take lollipop and put it in a glass container with hot water. And let it sit there.

What happens? The lollipop slowly dissolves into the water.

What you see there is saturation (or lack thereof) in action. When your pool water is unsaturated with calcium, it's like the lollipop in hot water, the calcium from your plaster will dissolve. When your pool water is over-saturated with calcium, it's like making rock candy, calcium (as calcium carbonate) will want to grow all over your pool surface. The CSI is nothing more than a measure of how over-saturated or under-saturated your water is with calcium carbonate. If your CSI is excessively positive, then there is a chance calcium scale will form under the right conditions. If your CSI is excessively negative, the water will dissolve calcium from any source it can find, eg, your plaster. Unlike rock candy which only depends on how much sugar you dissolve in water and what the temperature is, CSI also has to factor in pH and TA as well as some minor variations based on salt and borates.
helped me out as well! thanks

11. ## Re: Pool Math and CSI question

Originally Posted by TriPool
Thanks for information, that was my assumption as well that I could mostly keep levels and ignore CSI. FYI I have just a regular pool, no SWG. Being new I have been focusing on primarily on FC/CYA/PH.

Reviewing the docs, it looks like I must have been reading the CH on the vinyl pool (CH 0-350), not plaster (CH 250 - 350 ) My PB also mentioned a very wide range and I have assumed that 120 is okay. Looks like if I just raise that to 250-350 and leave PH at 7.6 or higher it gets me into a more reasonable range where I probably don't have to worry about CSI as you stated.

I have put baking soda in to raise TA, but when I do that it tend to drift back down pretty quickly (days) back to the 60 range where it seems to be stable, so I have been mostly leaving it there. I guess bringing that back up to the lower 70 range would also help.

Thanks for all the suggestions / help. I think this makes a bit more sense. Out of curiosity, how long does it take for an out of range CSI to cause problems? Is it days, weeks, or more of a long term situation?
Leaving your TA at 60 is fine, no need to fight that if that is where it wants to be.

It takes months or years for CSI to impact your pool. The problem is that it happens very slowly and is hard to notice until it gets bad, either scaling or etching. Then it is difficult to recover. Keeping your CSI in check, preferably slightly negative (-0.1 to -0.2), will make your plaster last a LOT longer, like 10 or more years longer.

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