Cal Hypo Strategy Advice & Price Comparison Math

[ol_whistle_britches]

FC 4.5 / CC 0 / CYA 45 / TA 110 / CH 275 / CSI +0.31 / Salt ~600

17Kgal IG Plaster (plaster totally spalled, circa 1998)

Need someone to double check my thought process here. Bought my houes and the pool got out of control before I could get moved in. Fired the pool boy because chem was out of whack and I got way different answers on past maintenance from the pool boy and the previous owner.

Just refilled my pool 1/12/25, ran a SLAM protocol, and am bringing everything on line and under control. Water looks gorgeous. I have low CH and I use 10% liquid chlorine. (I also need to bring TA down, but that’s easy enough.)

Pool Math says 18 gallons of 10% liquid chlorine will raise my FC 106 ppm. That’s 6 cases from Home Depot, equal to $120 in total. Pool Math also says 24 pounds of 65% cal hypo will raise FC 109 / CH 77 / salt 115. I can buy 24 lbs 68% cal hypo from Doheny’s for $102.

I get the feeling cal hypo is discouraged here, generally speaking, but in this case I’m tempted to buy a case of it and discontinue the liquid chlorine until I bring the CH up to where I want it (probably fine buying 24 lbs, which will put it around 325ppm). If I tried to raise it using calcium chlorate, I would have to add an equivalent 12 lbs, which will cost me at least $50 for a 25lb bucket. The way I see it, I just need to use cal hypo for a bit to slowly bring it into check. The salt addition is negligible for this temporary use, and I assume will be utilized anyways when I convert to SWG after my home warranty expires this year.

The way I see it, I have to buy the chlorine anyways so I might as well get two for the price of one and save ~$70. Am I reading this wrong? Better yet, given that the plaster job has already gone to pot, should I just ignore CH and CSI until I get the pool resurfaced sometime in the next 3 years? Do CH, TA and PH even really matter if the plaster’s shot and the water is pretty?

 

[proavia]

What is the pH, TA and CH of your fill water?
What is the source of your fill water (city, well, etc)?

Post a complete set of current test results from your TF-Pro.

FC
CC
pH
TA
CH
CYA
Water temperature

Seriously consider installing a SWG.

 

[PoolStored]

You don't indicate the pH and Temp of your pool. What are they?
To get a CSI of .3, your pH has to be 8 at a temp of 70.

A CH of 275 is just fine.

Your water temperature is likely low, and your CSI will just climb as your temperature climbs. Your CSI is already on the high end of the range. Adding more CH will just increase your CSI and the possibility of scale.

As @proavia indicates, test your fill water for TA and CH. If they are both high, you will not want to add calcium, and will have to manage your TA.

Your high pH, and TA are the cause of your CSI being high. Lowering TA to 80 would bring your CSI down by .2, and lowering pH by .2 from 8.0 would lower your CSI by about .2.

I would not add more calcium. Use liquid chlorine until you can reliable manage your TA 60-80 and manage your pH.

 

[Bperry]

FC 4.5 / CC 0 / CYA 45 / TA 110 / CH 275 / CSI +0.31 / Salt ~600

17Kgal IG Plaster (plaster totally spalled, circa 1998)

Need someone to double check my thought process here. Bought my houes and the pool got out of control before I could get moved in. Fired the pool boy because chem was out of whack and I got way different answers on past maintenance from the pool boy and the previous owner.

Just refilled my pool 1/12/25, ran a SLAM protocol, and am bringing everything on line and under control. Water looks gorgeous. I have low CH and I use 10% liquid chlorine. (I also need to bring TA down, but that’s easy enough.)

Pool Math says 18 gallons of 10% liquid chlorine will raise my FC 106 ppm. That’s 6 cases from Home Depot, equal to $120 in total. Pool Math also says 24 pounds of 65% cal hypo will raise FC 109 / CH 77 / salt 115. I can buy 24 lbs 68% cal hypo from Doheny’s for $102.

I get the feeling cal hypo is discouraged here, generally speaking, but in this case I’m tempted to buy a case of it and discontinue the liquid chlorine until I bring the CH up to where I want it (probably fine buying 24 lbs, which will put it around 325ppm). If I tried to raise it using calcium chlorate, I would have to add an equivalent 12 lbs, which will cost me at least $50 for a 25lb bucket. The way I see it, I just need to use cal hypo for a bit to slowly bring it into check. The salt addition is negligible for this temporary use, and I assume will be utilized anyways when I convert to SWG after my home warranty expires this year.

The way I see it, I have to buy the chlorine anyways so I might as well get two for the price of one and save ~$70. Am I reading this wrong? Better yet, given that the plaster job has already gone to pot, should I just ignore CH and CSI until I get the pool resurfaced sometime in the next 3 years? Do CH, TA and PH even really matter if the plaster’s shot and the water is pretty?

Calcium getting too high causes problems with equipment. Calcium being too low just affect plaster. So if your plaster is already done for, there’s no need to add more calcium. You already have plenty in there.

 

[ol_whistle_britches]

You don't indicate the pH and Temp of your pool. What are they?
To get a CSI of .3, your pH has to be 8 at a temp of 70.

A CH of 275 is just fine.

Your water temperature is likely low, and your CSI will just climb as your temperature climbs. Your CSI is already on the high end of the range. Adding more CH will just increase your CSI and the possibility of scale.

As @proavia indicates, test your fill water for TA and CH. If they are both high, you will not want to add calcium, and will have to manage your TA.

Your high pH, and TA are the cause of your CSI being high. Lowering TA to 80 would bring your CSI down by .2, and lowering pH by .2 from 8.0 would lower your CSI by about .2.

I would not add more calcium. Use liquid chlorine until you can reliable manage your TA 60-80 and manage your pH.

Thank you all for your responses.

It appears I did indeed forget to add the pH reading on the above test results. I do test it every time. It sits around 8.05 on my meter. Water sample was at 68 this morning.

Municipal fill water reads TA 90 / CH 125 / pH 8.1

Sounds like I can ignore CH being low given end of life plaster. Do I just ignore CSI until I replaster and continue to manage TA directly via acid? Will the fill water tend to consistently raise TA over time going forward? And given the characteristics of the fill water, would adding borates have a tendency to buffer the TA?

How often do you all find yourselves adding muriatic acid?

 

[PoolStored]

Sounds like I can ignore CH being low given end of life plaster.

I would test CH, and not let it get below 250. I don't care the condition of the plaster. Maintain CH will prolong the life of the plaster.

Do I just ignore CSI until I replaster and continue to manage TA directly via acid?

If we get your TA to ~60, your pH will be fairly stable around 7.8, and will give you a CSI that is slightly negative.

Do this, lower your pH to 7.4 with muriatic acid. Allow it to rise to 8. Reduce again. Continue this until your TA is 60-80. At that point, only lower the pH to 7.8 and it should be stable at 7.8 to 8.0.

Will the fill water tend to consistently raise TA over time going forward?

Yes, once you are below 90, but it should be manageable.
If your fill water is 90, how did it get to 110?

and given the characteristics of the fill water, would adding borates have a tendency to buffer the TA?

No. Borates buffer pH. I'd hold off on adding borates until you have more experience, understand the chemistry dynamics and can manage what you have. Ask me how I know...

As to frequency of acid additions, every pool is so different you can't compare yours to others. I add acid once a year. There are members that add daily, some weekly, some monthly, depending on test result and how their pool behaves.

 

[ol_whistle_britches]

If we get your TA to ~60, your pH will be fairly stable around 7.8, and will give you a CSI that is slightly negative.

Do this, lower your pH to 7.4 with muriatic acid. Allow it to rise to 8. Reduce again. Continue this until your TA is 60-80. At that point, only lower the pH to 7.8 and it should be stable at 7.8 to 8.0.

That I can do…

I would test CH, and not let it get below 250. I don't care the condition of the plaster. Maintain CH will prolong the life of the plaster.

Let me ask you this, how would CH go down at this point unless I started doing water changes?

If your fill water is 90, how did it get to 110?

I don’t quite know. I ran that test twice. I suspect it may be residual from the old pool water, as I probably did an 80% exchange. Otherwise I don’t know. I’d like to think I performed the tests properly. I watched the YouTube, followed instructions to a T, and practiced as good of chemistry procedures as I’m capable of, wiping the dropper and dropping until color ceases to change and what not. I triple rinse everything I use.

 

[PoolStored]

Let me ask you this, how would CH go down at this point unless I started doing water changes?

275 is just fine, no need to lower. Only water exchange or reverse osmosis or replacement with lower CH water will reduce CH (drain and replace). With a CH of 125 on your fill water your CH increase will be small with fill water.

I suspect it may be residual from the old pool water, as I probably did an 80% exchange. Otherwise I don’t know. I’d like to think I performed the tests properly. I watched the YouTube, followed instructions to a T, and practiced as good of chemistry procedures as I’m capable of, wiping the dropper and dropping until color ceases to change and what not. I triple rinse everything I use.

Your tests are likely just fine. When you clean your vials, use isopropyl alcohol and dry. If you ever convert to SWG, use ammonia in the salt test to clean.

If you ever need them, these are available...

Extended Test Kit Directions Archives

www.troublefreepool.com