CH question

Bwdonohues58

Gold Supporter
In The Industry
Apr 22, 2019
50
Homer, AK
I have an indoor aquatic physical therapy pool, 10,300 gallons (3 1/2' to 4' deep). We opened on July 11 in Homer, AK. The pool walls are 100% small glass tiles with epoxy grout. My CH is around 360 and TA around 80. 12.5% liquid chlorine. I try to keep the pH at 7.5 but it does creep up on me so I periodically add dry acid. Using the pool math calculator, my CSI comes out to around +0.26, which is within the OK range, but I do get calcium on the dark blue tiles above the waterline. I've read that the high-side CSI limit is around +.3, so I am pushing on that. My question has to do with how to lower the CSI into a slightly negative value but still within the OK range, maybe around -0.1 to -0.2. Will make the water less likely to deposit white stuff on the tiles? I also get white residue on my blue pool cover. I am thinking about draining off 1-1/2' or 2' of water and filling it back up with clear water to lower the CH, then balance out the other values. Does anyone think that making the water slightly acidic and less calcium rich will have any adverse effects? I believe that epoxy grout is pretty resistant to slight acidity. BTW, I have no windows in the pool room so I don't use CYA. The pool consumes about 11 oz. liquid chlorine daily, so a 15 gallon drum lasts about 4 months. The chlorine is fed with a Stenner pump/tank combo.
 

Texas Splash

Mod Squad
TFP Expert
LifeTime Supporter
"58", perhaps I can address a few of your concerns:
1. To answer your basic question first .... sure, the concept of water being slightly aggressive in nature (negative CSI) should help to reduce or prevent scale build up. However ....... :)
2. Before that though, how are you testing your water? Can you update your signature please with all of your pool and equipment info? Also include that this is an indoor pool and which test kit you are using. Confirming accurate test results is a must.
3. Even with an indoor pool, you should plan to retain a small CYA of about 20 or so. Reason being that with no CYA, he chlorine is "extremely" strong and harsh with no buffering protection at all.
4. Your Poolmath log doesn't have much history, so if you could post all of your test results as follows, that will be a great starting point along with the questions above. We'll do our best to help.

FC
CC
CYA
PH
TA
CH
Also include water temp.
 

Texas Splash

Mod Squad
TFP Expert
LifeTime Supporter
For what it's worth, you might double check your Poolmath calculations. I'm getting a negative -0.28 with the numbers you quoted above. Could there be a typo somewhere?

Also, do you have muriatic acid available in your area? Dry acid tends to add sulfates which can be troublesome over time.
 

Bwdonohues58

Gold Supporter
In The Industry
Apr 22, 2019
50
Homer, AK
"58", perhaps I can address a few of your concerns:
1. To answer your basic question first .... sure, the concept of water being slightly aggressive in nature (negative CSI) should help to reduce or prevent scale build up. However ....... :)
2. Before that though, how are you testing your water? Can you update your signature please with all of your pool and equipment info? Also include that this is an indoor pool and which test kit you are using. Confirming accurate test results is a must.
3. Even with an indoor pool, you should plan to retain a small CYA of about 20 or so. Reason being that with no CYA, he chlorine is "extremely" strong and harsh with no buffering protection at all.
4. Your Poolmath log doesn't have much history, so if you could post all of your test results as follows, that will be a great starting point along with the questions above. We'll do our best to help.

FC
CC
CYA
PH
TA
CH
Also include water temp.
For what it's worth, you might double check your Poolmath calculations. I'm getting a negative -0.28 with the numbers you quoted above. Could there be a typo somewhere?

Also, do you have muriatic acid available in your area? Dry acid tends to add sulfates which can be troublesome over time.
FC 1.5
CC 2.0
CYA 0
PH 7.5-7.6
CH 360
TA 80
Water temp 92-96. Usually around 94.

I have an AOP and UV so the chlorine is just in case. Numerous coliform tests all come up zero.
 

Texas Splash

Mod Squad
TFP Expert
LifeTime Supporter
Based on those numbers, which include the water temp (CSI of about 0.22), that could explain why you are seeing some instances of scaling around the pool or waterline. While your numbers are otherwise well within acceptable ranges, you might consider one or more of the following:
- Partial water exchange to lower CH to about 300
- Letting the TA fall to about 60 and maintaining the pH at about 7.4-7.5.
- Lower water temp a bit

You probably know from using the PoolMath APP that besides the pH, your water temp plays a huge role in the propensity to develop scale. For outdoor pools in hot areas it's a problem every summer. But if you can keep the water temp under 94 that should also help.

On a side note, I would still encourage you to add a little stabilizer. Something in the 15-20 range if possible. Even 1-2 ppm of free chlorine is extremely harsh if left un-buffered. The other thing is your CC level. Its a bit elevated. Anything over 1.0 for us is a sign that the water is under stress from excessive organics not being kills or oxidized effectively. You may want to keep a close eye on that to ensure it's not an early sign of algae. Hope this all helps. If you have any other questions, please let us know.
 

Bwdonohues58

Gold Supporter
In The Industry
Apr 22, 2019
50
Homer, AK
Thanks, Splash. I'll do as you recommend. I really like the pool as is, except for the white stuff. One problem I have is that I am using a Lamotte Color Q Pro and it gives widely different readings. I see that a lot of people have this issue. What I have done is to do 2 or 3 repeated tests and sort of averaging the result. The Color Q is what I really want but it's not very accurate. I also have a Taylor setup but the color comparison is very approximate as well. All the pool users here are very happy with the water but I think that I got fooled into putting in too much calcium chloride (32 lb in 10,300 gallons) at the git-go. The Lamotte Color Q Pro consistently told me that I had a CH of under 200 so I kept adding CaCl until it was over 350. The Taylor setup set me straight. I think you are absolutely right about the TA. I just ordered two cases of four-one gallon packs of muriatic acid as I am sure you are right about the dry acid. Thanks for the help.
 
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Dirk

Gold Supporter
TFP Guide
Nov 12, 2017
7,216
Central California
Please work on your signature, and include which Taylor kit you have. If it is one of the two we recommend, and you use it exclusively, you wouldn't be averaging test results or inadvertently overdosing your pool.

 

Bwdonohues58

Gold Supporter
In The Industry
Apr 22, 2019
50
Homer, AK
On Saturday, I pumped out about 3200 gallons and had the water truck refill it with fresh. CH is now 260, which I still believe is about 10% higher than I would prefer. On Friday, I'll drain off 4.5" of pool water (my average depth is only 45") which will take about 45 minutes plus adding it back with the hose will take around 2-½ hours. No big deal. This will put the CH down to about 240. I would like to keep the PH at 7.5 using muriatic acid (I bought some at the pure water place) and keep the TA at 60-65. In my experience, this involves adding acid, then baking soda, acid then baking soda, on and on. Is this just a fact of life with pools? Thanks for all your help. I cleaned off the white stuff from the waterline tiles (using some leftover dry acid) and it all looks like new again
 

Texas Splash

Mod Squad
TFP Expert
LifeTime Supporter
Good to hear you were able to lower the CH a bit. Yeah, the desire to maintain a pH around 7.5 may require more frequent acid treatments thereby lowering the TA a little over time - hence the baking soda bump. But it's certainly manageable. Sounds like you have a handle on things.