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