Does all Trichlor dispense CYA?

[AnnaK]

I use a product called Seaboard Slo Tab 8 in an inline feeder when I have to leave the pool unattended for a few days. The container says "stabilized trichlor" and "89% available chlorine" -- whatever that means. There is no mention of CYA as an ingredient anywhere. Does trichlor somehow break down into cyanuric acid?

My CYA level has dropped from 60 at the beginning of the season after I added some to 35-40 now. One pool store told me it was 100 in May and 'dontcha worry yer head off, li'l lady' without any comment at all about increasing my chlorine levels, though they did want me to add 42 pounds of calcium (to my vinyl pool). Sigh. I ordered a Blue Devil test kit and have been checking once a month, and it has apparently leveled out at 35-40 which was the reading last month as well.

If the Slo Tab 8 add CYA, would I not see an increase in stabilizer? Or is the increase small enough to be negated by backfilling and rain? The pH is holding steady at 7.5, TA is 110, FC ranges between 3 and 5, CC has always been 0.

I clearly do not have a handle on how trichlor affects my water other than the water is clean, soft, sparkling and the bottom never feels slick.

 

[duraleigh]

Occasional use of trichlor adds very little CYA so your thinking of backwash and rain refills negating it is probably correct. That said, all trichlor adds CYA...frequently called stabilizer.

 

[chem geek]

Trichlor + 3H₂O --> CYA + 3HOCl
Trichlor + Water --> Cyanuric Acid + Hypochlorous Acid (chlorine)

For Trichlor, the two weak acids cause the pH to drop and when the chlorine gets used up the pH drops further -- hence, Trichlor is very acidic.

Dichlor•2H₂O + H₂O --> CYA + 2HOCl + Na⁺ + OH^-
Dichlor Dihydrate + Water --> Cyanuric Acid + Hypochlorous Acid (chlorine) + Sodium Ion + Hydroxide Ion

For Dichlor, the two weak acids combine with the sodium hydroxide (lye) for a net result that slightly decreases the pH, but when the chlorine gets used up the pH drops further. Hence, Dichlor is acidic, but not as much as Trichlor.

 

[AnnaK]

Excellent, Richard. Thank you very much!

I had a horrible time earlier this season with high TA and creeping pH. I added HCl and aerated but the pH would go up again. Then I began using the trichlor feeder at a low setting and the pH has been holding at 7.5 for over a week now. TA dropped from 200 to 110 and also holding for a week.

I'm doing the trichlor thing as a test because I'll have to be gone for a while later in the year with no one to check on the pool; my goal is to reach a point where the trichlor will manage sanitation without intervention in the absence of a swimmer load.

Anna

 

[Rangeball]

Anna, aeration is done to increase PH while keeping TA lowered, via outgassing of CO2. The goal is to get TA to a point that PH stays stable where you want it.

Trichlor is very acidic and as such will knock your PH down. If you have elevated TA, this could lead to a PH hold, which would be great if it doesn't lead to increase CYA, which it can, over time.

As long as you manage CYA either through dillution when it gets to high or stopping trichlor use and keep FC where it needs to be, you should have a workable goal.

 

[AnnaK]

Thanks for validating my plan, Rangeball. I'm pleased with the constancy of the pH and TA readings so far. At this point I occasionally add some bleach to keep the FC in line with the CYA readings and I have another month with this program, enough time to reach a level of confidence to reasonably predict for the prolonged absence.

Anna