Thoughts on CSI and FC

mkmscr

Well-known member
Mar 1, 2013
72
Charlotte, USA
Curious, TFP pool app is suggesting my CSI is setting conditions for corrosion to begin with a CSI at -0.6 is that correct? My PH is about 7.6 and my TA is about 65. CH is a little low at 250. I understand PH can help adjust CSI but I generally don’t go much higher. Thoughts or am I okay?

Lastly, FC has been around 8.0 this winter while using the tri chlor floating pucks. I have those floating around until my SWG can fire up again. Should I be worried it’s too high?

Lastly, lastly, thoughts on algaecides? I don’t seemingly have any issues and I always keep my FC on point but curious if I should introduce them. I get worried adding anything additional with kids and thr dog always in the pool during the warmer months.

Gunite/plaster pool/pebble sheen/salt (not currently active, too cold)
 

Jimrahbe

Mod Squad
TFP Expert
LifeTime Supporter
Jul 7, 2014
18,736
Bedford, TX
M,

Why in the world do you run your pH at 7.6, when most SWCG pools like 7.8 or 7.9.. ?? I did not run the numbers, but suspect that letting your pH come up will put your CSI right where you want to be???

There is no downside to running your FC a little high, so I don't see that as an issue.

If you are running pucks, I'd want to know what the CYA is to make sure it never goes too high..

Thanks,

Jim R.
 

JJ_Tex

Bronze Supporter
Jul 17, 2019
1,524
Prosper, TX (DFW)
TFP does not normally advocate the use of algeacides as they can introduce heavy metals that can cause staining down the road. Focus on your FC/CYA relationship on this chart (you also didnt mention your CYA levels, so there is no way to tell if 8.0 is in your target range or not) and you should not have to worry about algae.

 

jseyfert3

Bronze Supporter
Oct 20, 2017
939
South-Central WI
Curious, TFP pool app is suggesting my CSI is setting conditions for corrosion to begin with a CSI at -0.6 is that correct?
When my CSI is from -0.6 to -0.3, my poolmath app says "You should avoid CSI of less that -0.3 for prolonged periods of time to avoid the potential of corrosion to plaster, tile, stone and pebble pools."

When less than -0.6, it says: "Less than -0.6 suggestions corrosion is likely for plaster, tile, stone, and pebble pools."

Summary: You should aim to keep your pool at -0.3 and above for long periods of time.
 

mas985

TFP Expert
LifeTime Supporter
May 3, 2007
13,700
Pleasanton, CA
Curious, TFP pool app is suggesting my CSI is setting conditions for corrosion to begin with a CSI at -0.6 is that correct?
Technically CSI is an indicator for scale and not etching although by extension there should be a corollary to etching. Etching doesn't start at a particular CSI level but is related to the probability of occurrence. So a CSI of -0.6 would theoretically have twice the etching potential as a CSI of -0.3 (log scale) but both would still be extremely slow. Based upon some testing by @onBalance, even CSI below -0.6 showed very slow etching.

 

mkmscr

Well-known member
Mar 1, 2013
72
Charlotte, USA
M,

Why in the world do you run your pH at 7.6, when most SWCG pools like 7.8 or 7.9.. ?? I did not run the numbers, but suspect that letting your pH come up will put your CSI right where you want to be???

There is no downside to running your FC a little high, so I don't see that as an issue.

If you are running pucks, I'd want to know what the CYA is to make sure it never goes too high..

Thanks,

Jim R.
Hey Jim,
Running pucks until the SWG will kick on when the warmer temps come around. I think my SWG turns off at a certain temp. My CYA is around 65 but I am keeping a close on on my CYA so that does not get out of control while using tri-chlor pucks.

I normally aim for 7.8ish for the PH but I have negative edge that runs a few hours each day and a sheer descent (winterized for now) and when those are running my PH creeps up naturally. So I usually have to add a little MA in the summer to move it down to 7.6ish then it will creep back up with all the aeration. With the winter upon us they are not running as much so I should let the PH and TA float a bit higher. Although I have not added any MA so its just hovering naturally around 7.7. As I said I think I am going to let the PH and TA float up a little higher and that will bring my CSI to negative .3 or less according to the TFP app. Currently my TA is 65.
 

mkmscr

Well-known member
Mar 1, 2013
72
Charlotte, USA
TFP does not normally advocate the use of algeacides as they can introduce heavy metals that can cause staining down the road. Focus on your FC/CYA relationship on this chart (you also didnt mention your CYA levels, so there is no way to tell if 8.0 is in your target range or not) and you should not have to worry about algae.

I am keeping the CYA around 65 -70ish.
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
32,518
Laughlin, NV
The trichlor pucks you are using are very acidic. They are reducing your pH and TA. Stop using them and use liquid chlorine.
 

mkmscr

Well-known member
Mar 1, 2013
72
Charlotte, USA
The trichlor pucks you are using are very acidic. They are reducing your pH and TA. Stop using them and use liquid chlorine.
Interesting...probably explains why my PH has not been creeping up. I just assumed it was the lack of running the water features. Do they make a chlorine puck, no other additives? Yes I am being lazy :)
 

jseyfert3

Bronze Supporter
Oct 20, 2017
939
South-Central WI
Interesting...probably explains why my PH has not been creeping up. I just assumed it was the lack of running the water features. Do they make a chlorine puck, no other additives? Yes I am being lazy :)
Nope. Chlorine comes in 7 forms for pools (only 6 for residential pools):
  1. SWCG - generates chlorine from salt in the pool. Does not work in the winter (obviously). Does not change pH/TA.
  2. Dichloroisocyanuric acid (dichlor) - usually a powder. Adds both FC and CYA. Mildly acidic, so it can slowly lower pH/TA.
  3. Trichloroisocyanuric acid (trichlor) - usually in puck form. Adds both FC and CYA. Very acidic, so it can rapidly lower pH/TA.
  4. Sodium hypochlorite - liquid. Commonly referred to as "liquid chlorine" (bleach). Adds FC only (and a tiny bit of salt, but so does everything else on this list). Does not change pH/TA.
  5. Calcium hypochlorite (cal-hypo) - usually a powder. Adds both FC and CH. Not commonly used since it adds CH and most people have too much CH, but is handy if you are in the rare set of people who need to occasionally add CH. Does not change pH/TA.
  6. Lithium hypochlorite (lithium hypo) - usually a powder. Adds both FC and Li+ ions (which doesn't affect water chemistry). Only form of "dry" chlorine that doesn't change pH/TA/CH/CYA. Not commonly used as it's very expensive.
  7. Chlorine gas - dangerous to handle/store, expensive equipment needed, needs permits. Not available for residential pools. Only used for commercial pools or municipal water sanitation.
If you want to be ultimately lazy, and adding liquid chlorine once a week in the winter till your SWCG comes back online is too much work, you could get a Stenner pump or similar to auto-dose liquid chlorine, but you'd still need to occasionally check your FC level to make sure everything is in order. And that's ultimately laziness if you buy a $300 pump to do something you only have to do once a week or so :wink: (usually Stenner pumps are used to dose liquid chlorine in the summer as an alternative to a SWCG).
 

JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
17,205
Tucson, AZ
Pucks are fine in the winter. They will dissolve very slowly and keep your FC very stable. As long as you are aware of and testing CYA, it’s not a big deal. In the winter my pool uses very little FC. You can look at my logs but I think I went an entire month between additions and I only lost 2ppm FC. Pucks work fine too. Last winter I put four in the floater and I think I went almost 5 weeks before they dissolved.