Cal-Hypo Dosing Inconsistancies

[Scoop]

I have a question about Cal-Hypo and FC dosing calculations.

Background:

- 15,000 Gal Plaster Pool
- D.E. Filter 36 Sq Ft
- FC Testing tools: R-0870/71 FAS-DPD with Taylor 9198 vial (10mL sample) and SpeedStir.


I've been using the TFP dosing method (Bleach & FC/CYA ratios) for about 2 years. The pool's been on cruise control; no algae issues, water always perfect, etc.

I tested my CH recently and it was at 225, below the recommended range (250-350).

I have a bucket of Cal-Hypo 68% which I haven't used in over 2 years. I figured I'd dose a while with it to add CH and dose at the same time.

I used the Pool Math calculator for Cal-Hypo dosing but hadn't used this for Cal-Hypo in years so I don't recall how close the actual FC results were back when I was using Cal-Hypo to dose regularly.

Here's a screencap with my usual pool #'s in the "Now" column. I highlighted the calculated "Target" Cal-Hypo # for the desired dose. My CYA level is on the low side. I plan on raising that soon.



Here's what I've seen with the Cal-Hypo dosing:

I added 13-14 Oz to raise the FC level to about 7 - 7.5 .

I tested the FC the next day and the result was 4.0 , raising the FC +1 instead of the calculated +4 - 4.5 .

I figured it was an anomoly so I dosed again, using about 20 Oz Cal-Hypo to add a calculated +7 FC. I tested again the next day. Instead of a result of calculated 11 FC, I measured 6.5 FC . That meant I was getting approx +1 FC to about 8 Oz of Cal-Hypo.

I tested the next day and got 3.0 FC. That indicated a depletion rate of 3.5 in one day which wasn't normal for my pool (using Bleach the last 2 years) for this time of year.

I ran an OCLT to insure all was ok with the water, that nothing was consuming a larger than normal amount of FC. OCLT result: 0 , no FC loss overnight. I also checked CC levels the last couple of days. The CC tests were good, either 0 or .5 .

The next day, I resumed dosing with Bleach to test my dosing, FC test, and calculated dose values.

I retested FC several hours later. All was perfect, Bleach calculated dose vs actual FAS-DPD test results aligned perfectly and the depletion rate was as expected for my pool at this time of year.


CH Testing: I used my original R-0011L dye, which is over 3 years old. I think it's still good but I bought a new R-0011L bottle to verify the CH test. Both bottle's tests results were identical.

The question I have is about Cal-Hypo shelf life and if the hypochlorite can lose its potency over time.

I wanted to try and use the Cal-Hypo to increase the CH level without buying calcium chloride, Hardness additive, etc.

Has anyone recently used Cal-Hypo to dose their pool and has seen similar dosing inconsistancies as I have seen with these test results?

 

[jblizzle]

I think you should read test the chlorine levels after only an hour to of adding the powder. It is possible that waiting a day is allowing the chlorine to be consumed by something. Although I do see that you are passing the oclt.

 

[smackdab]

Pool Math goes through a conversion from weight (14 oz weight in your case) to volume (13 fl oz volume in your case). The conversion requires the bulk density of the product, which can vary from product to product so something can be lost in this conversion but I don't see it being that far off. Bleach and the other liquids don't require this type of conversion because they are volume. If looking for a spot on number with the dry stuff then the weight is what you want to go by. If you have a scale, measure out 14oz weight then pour that over in a measuring cup and see if it comes out to 13 fl oz volume.

Calcium Hypochlorite can degrade but it takes alot longer than what bleach will. If the Cal-Hypo did loose some of its chlorine, you would still have put the same amount of calcium in the pool for that amount.

You should test about an hour after dosing to see what the FC went up by. Waiting until the next day just allows time for something to eat away your FC.

 

[Scoop]

jblizzle, smackdab, Thanks for the info.

I don't have a small scale so I've been relying on the Pool Math calculated "volume" calculation and have been using the scoop that came with the Cal Hypo product.

It looks like I encountered some kind of anomoly the last couple of days. Here's what I did yesterday a few minutes before sunset and this morning right before sunrise:

Yesterday evening, about 30 min's before sunset (no direct sunlight in my pool):

- Checked FC with FAS-DPD: 3.5 . Previous test Thu 03/24 (right before dosing with Bleach) was also 3.5 , verifying my typical FC depletion rate/day for this time of year, around 1.5/day .

- Dosed with 32 Oz Cal Hypo, right before sunset. Calculated Pool Math expected results were +10.5 FC, resulting in 14.0 FC the next morning.

- Checked FC this norning a few minutes before sunrise (FAS-DPD) : 13.5

I've always thought that Pool Math calculater was amazing. It's been right on target for all of my tests the past few years.

I guess I was losing an unusual amount of FC for 1-2 days, or made a mistake somewhere during those dosing's / tests.

I'll check my daily depletion rates for 2-3 days to see if there's any difference between Bleach and Cal Hypo depletion rates.

I wouldn't expect any differences but it'll be interesting to see the results as my Bleach depletion rates have always been consistant and predictabe since I switched to Bleach a couple of years ago.

I'm not sure how much Cal Hypo will be needed to get my CH level back in midrange (~300) .

 

[Richard320]

I'm not sure how much Cal Hypo will be needed to get my CH level back in midrange (~300) .

Scroll down to Effects of adding Chemicals at the bottom of poolmath, after you've input your pool volume up at the top. Plug 16 oz in the quantity and select your Cal-hypo from the dropdown. It'll show you how much CH each pound adds. Then some simple arithmetic will tell you how many pounds you need to hit your target. Then just chlorinate normally until you've added that much Cal-hypo and switch back to bleach.

 

[Scoop]

Scroll down to Effects of adding Chemicals at the bottom of poolmath, after you've input your pool volume up at the top. Plug 16 oz in the quantity and select your Cal-hypo from the dropdown. It'll show you how much CH each pound adds. Then some simple arithmetic will tell you how many pounds you need to hit your target. Then just chlorinate normally until you've added that much Cal-hypo and switch back to bleach.

Thanks, I forgot about that section of the Pool Math page.

Here's something that seems strange to me:

I tested my 12-hr FC Depletion Rate just before sunset (no sunlight on pool); 10.0 , which was a total of -3.5 FC depletion since sunrise today. That rate was identical to earlier this week when I switched to Cal Hypo. I checked the Depletion Rate from Tue-Wed and it was also -3.5 .

During the last couple of years since switching to Bleach, the most FC I've seen depleted in a day is usually around -2.25 to -2.75 during the middle of the summer months here in Dallas.

I wonder if Bleach chlorine usage properties differs from the chlorine included in Cal Hypo. I'd think it should be the same with both varieties.

I'll test daily Depletion rates for awhile to see if there's a difference with Bleach or Cal Hypo.

 

[Richard320]

The depletion could be related to a) insufficient CYA. It could have gotten diluted over the winter from rains
b) Organic debris. That includes stuff that might be inside the filter where you don't see it.

 

[Scoop]

Thanks for the info.

Regarding CYA, I dosed with solid CYA last Friday to raise it from 30 to 40 . I'll test CYA this Friday.

Organics in Filter, interesting point. The part that isn't making sense to me is that the Cal Hypo chlorine seems to deplete faster than Bleach chlorine.

I'll know more when I compare day-to-day Depletion Rates between the 2 dosing mechanisms over the next few days.