Low CSI but I think numbers for tests look reasonable

#1
This is my first post so I apologize for any misses on protocol for asking for help.

I just had a pool installed and handed over to me in late December in the San Diego area. It's a ~25k gallon SWG fed pool. It's been chilly here for a while and a rather wet "winter" for this area. I have downloaded PoolMath on my phone and have input a couple of results to it. A few days ago my pH was high at 8.0. So I added MA to it per the suggestions on the app. CSI measured at that time (before adding MA) was -0.51. Pool is nice and crystal clear. Pump runs 8hrs a day everyday. Nothing suggest algae at all. I brush it a few times a week. Have definitely had rain here a lot though over the past 2 weeks.

But today I tested the water and got the following results:
FC = 4.6
CC = 0
pH = 7.4
TA = 60
CH = 220
CYA = 80
Salt = 3000
Temp = 51
CSI = -1.07

The last time I tested the water a few days ago CSI was at -0.51. I am worried that such a low CSI will start to show scaling but perhaps I am just watching it too closely? Hoping someone with more experience than I can shed some insight into why/how I can get my CSI up to +/-0.6 range (preferably closer to 0.

Any help will be appreciated.
 

mknauss

Mod Squad
May 3, 2014
12,830
Laughlin, NV
#2
Welcome to the forum!
With cold water your CSI can get quite negative. Negative CSI (below -0.6) implies the water is aggressive to plaster. If left for long periods of time it can pull calcium from your plaster and damage it. Positive CSI (above 0.6) implies scaling tendency.

It would be best during the cold water times to leave your pH at 7.8 or 8. Your CH is on the low end of the range but that will climb this summer as you add water due to evaporation.

Have you tested the pH, TA, and CH of your fill water? It is a great idea to do and record that in your app.

I suggest you read ABC's of Pool Water Chemistry and consider reviewing the entire Pool School eBook.
 
Likes: Jedisparky

mknauss

Mod Squad
May 3, 2014
12,830
Laughlin, NV
#3
Can you fill out your Signature? The best way to raise your pH a bit is through aeration. Depending on what type of pool and equipment you have you may be able to easily do that.
 

ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
3,793
Northern NJ
#4
Please complete your signature with details of your pool. It will help us help you.

Let your pH drift up to 7.8. That will raise your CSI. Your CSI is low due to the cold water. It will rise as the water warms.

Your CH is on the low side and raising it a bit will also raise your CSI.
 
#5
Thanks guys! Definitely looking forward to warmer weather here! I will let the pH drift up to the higher range.
I planned on using the spa this weekend so maybe that will help aerate the water?

Haven't tested my fill water yet actually so maybe this weekend when the weather gets better I can do that. Good idea to know what I have to compensate for on a regular basis. It's on an autofill so who knows how much water that is actually putting into the pool.

Also filled out the signature so hopefully that helps. Thanks again for the help and I'll test the pH/FC/TA again this weekend to see if no rain and the sunshine helps.
 

mknauss

Mod Squad
May 3, 2014
12,830
Laughlin, NV
#6
Thank you on the signature.

Running the spa definitely aerates the water. It should raise your pH a bit.

When you get the fill water results post them. I suspect they will be higher in CH and TA.
 
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#10
Hey guys. Tested my pool for FC and pH today now that it's had some sun. I also cleaned out the pump skimmer basket of a small amount leaves that were in there.
FC = 4.0
pH = 7.6
Temp = 53

I also tested my fill water for pH, TA, and CH. Results below.
pH = +8.0 (the Taylor colors only go to 8 but it was deeper red than 8.0)
TA = 110
CH = 210

I may add some Chlorine to the pool to get it better than the minimum of 4. I'd like to see it closer to 6.
I'll let the pH get to 7.8 before I start to control it assuming it would continue to creep up.

Hopefully this helps.

Also, RoyR, my PB dumped a bottle of BioDex Stabilizer in the pool as part of the handover in late December. I haven't added any CYA since. I have only added Chlorine, MA, and of course the initial salt to get it to 3000ppm when I happened to notice the numbers getting too crazy. Admittedly I have sometimes only checked the water once a week on some weeks.
 

mknauss

Mod Squad
May 3, 2014
12,830
Laughlin, NV
#11
Your fill water will continually push your pH and TA up. So you will be adding muriatic acid on a very regular basis. Your CH will also climb over time.

Your PB had to dump over 260 oz (16+ lbs) of dry CYA into the pool to get to 80 ppm CYA. Are you sure that is the only CYA containing product that was added?
 
#14
I can try to recheck my CYA as the 80 reading was like 2 weeks ago and my wife did that one. Maybe with the rain and the overflow draining lowered it although very little sunshine in that timespan. Or maybe she misread the results?
Will do that tomorrow but I am not sure you usually have to keep checking that CYA all of the time right? That should be fairly consistent with slight drift downward over time with UV hitting it right?
 
#15
Also just remembered the PB put a couple of pucks in the skimmer. I remember they took a few weeks to dissolve and I didn't add any since. I just found the tub they came in so I checked and it looks like trichlor pucks. I assume that's probably a big source of any CYA?
 

mknauss

Mod Squad
May 3, 2014
12,830
Laughlin, NV
#17
A couple pucks is not that much.

I would check the CYA before assuming it is there.
When you do the CYA test, try this next time.
Once you have your solution ready, back to the sun, etc. Fill the vial to a line, say 80, lower the vial to your waist level and glance for the dot, you see it, add solution to the 70 line, glance, see it, repeat until you no longer see it with a glance. Then use the CYA value one step above the line you read. So if you stopped at 50, use 60 ppm CYA.

The vial is in logarithmic scale. So it is not viable to interpolate between the lines. Just use the whole numbers, such as 50, 40, 30, ....
 
Likes: Jedisparky
#18
Thanks again guys for the help with this. I definitely did the CYA test wrong the first time (looked straight down on it and looked really hard for the dot) so I followed your way and my CYA is at 60. Here are the latest results.

FC = 5.6
CC = 0
pH = 7.6
CYA = 60
Temp = 53F
CSI = -0.80
 

Jedisparky

Silver Supporter
Mar 9, 2017
131
L.A. CA
#19
A couple pucks is not that much.

I would check the CYA before assuming it is there.
When you do the CYA test, try this next time.
Once you have your solution ready, back to the sun, etc. Fill the vial to a line, say 80, lower the vial to your waist level and glance for the dot, you see it, add solution to the 70 line, glance, see it, repeat until you no longer see it with a glance. Then use the CYA value one step above the line you read. So if you stopped at 50, use 60 ppm CYA.

The vial is in logarithmic scale. So it is not viable to interpolate between the lines. Just use the whole numbers, such as 50, 40, 30, ....
Wow, Thanks! This is such great information. It's always been tough for me to "feel" like I got an accurate CYA because my technique seemed unsure, unclear. This is a rock solid testing method.

Thanks
Michael