Tablet recommendations don't add up?

[mwpow3ll]

First, I want to start by saying that I have reduced my CYA over the last year to 35ish, and I am doing a trial run on liquid chlorine only; however, I am puzzled by some calculations.

The label to my 3" Chlorine tablet container indicates 5.495 ppm of chlorine per 10,000 us gallons and recommends 2 tablets per week.

Assuming CYA is 30, Min FC is 2.25, and an avg of 2 ppm FC loss per day, 2.95 tablets would be required to last 7 days. Even reducing the week to 5 days with a min FC loss of 2 still requires 2.18 - 2.23 tablets.

The only way I can get their recommendations to match was assuming:
- 1.8 ppm FC loss / day, 5 days / week, and a Min FC of 2 ppm
- 1.75 ppm FC loss / day, 5 days / week, and a Min FC of 2.25 ppm
- 1.25 ppm FC loss / day, 7 days / week, and a Min FC of 2.25 ppm

I can't imagine a 1.25 ppm FC loss / day as being normal; so, I am leaning towards the 1.75 ppm FC loss at 5 days, but I guess the next question is, what would be a normal FC loss / day? I use to see anywhere from 1.5 - 2 ppm when using the tablets, but now switching to liquid I am seeing 2-3 ppm.

My reasons for trying to perform these calculations is that I am thinking a combination of tablet & liquid chlorine is best since it will add some CYA at a much slower rate, removing my need to buy stabilizer. It will also reduce my dependency on liquid chlorine so that I can get some of my garage space back, because even using 12% 1 US GAL liquid chlorine requires a lot of space / trips to the store for a 4-month pool cycle.

 

[Richard320]

I think you're overthinking things.

Go check out Effects of Adding Chemicals at the bottom of poolmath. It tells you what each pound of trichlor will do to your pool chemistry. If you suffer from high TA and constant pH rise, great! Trichlor is acidic. It will reduce your acid demand. Just work backwards from your CYA goal and figure up how many pounds of pucks will take your CYA where you want and use them until you reach the target, then switch to bleach.

If you don't have high TA and rising pH, you run the risk of lowering both too much with pucks, which means you have to start adding more chemicals, which will cost you.

I don't have a huge amount of space devoted to my pool chemicals. Less than the lawnmower takes. I get 12.5% bleach in 4 gallon returnable crates. I use about a quart a day during the summer, so one crate every two weeks or so. You'll use more, since your pool is bigger. And your pool may get more use; I have no kids in residence. But it's not a huge amount of bleach, and it degrades with heat and time, so you don't want to keep too much on hand anyway.