Using Tri-Chlor to start season

My in-laws gave me a bucket of Tri-chlor pucks that they don't need anymore (tore down their pool). When I uncovered my pool from the winter, there was no CYA present. As I filled up the pool for the season (had been drained below return line), I hit it with one gallon of 12.5% liquid chlorine. Since then, I have added the Tri-chlor to the skimmer basket. Took about 2 days for 2 pucks to disintegrate. I tested for CYA again, and still no reading on my Taylor test kit. Based on that, its looking like I can pretty much use this whole bucket before I start to see any CYA readings. I do have some straight CYA granules I can use after the Tri-chlor is gone, I just thought I would get at least some reading after the first couple pucks. My free chlorine was very low when I tested it as well. Should I get the free chlorine up and the combined chlorine to zero before I start using the pucks? Will that allow the CYA to come up faster?

Forgot to mention...pool is roughly 10,000 gallons, 12x24 in-ground.

For every 10ppm of Free Chlorine the pucks add, they will add 6ppm of CYA. Be sure to watch your pH as well, as pucks are EXTREMELY acidic. I'd spend $10 and buy a floater for the pucks rather than put them in the skimmer, where they can clog the system and wash components with a lot of acid if the pump is off.

Be patient when adding CYA.

In a 10,000 gallon pool, each 3" tri-chlor puck (~8 oz) will have the following effect on your water assuming your TA is within normal ranges and assuming they are 99% tri-chlor (have you checked the ingredients?):

Raise FC by 5.5ppm
Raise CYA by 3.3ppm
Lower pH by 0.29ppm
Raise Salt by 4.5ppm

The above assumes a fast dissolution rate which, as you can see, does not happen. A better way to start your pool would be to raise your CYA to the lowest value you want in a season (example would be 30ppm) using powdered stabilizer and shock-clean your pool assuming you are at your target CYA level. You can then use the pucks for chlorination until your CYA maxes out to 50ppm (would only take about 6-10 pucks to max out).

Save the bucket of tablets for vacation time and when you have to ignore your pool for a few days. They will last a long time if you keep them in a tightly sealed bucket in a cool dry place.

This is great information!

I was trying to find this on the label for the trichlor pucks, and they don't list it at all. The guys at the pool store had it all wrong, didn't realize that the ratio of chlorine to CYA is fixed and said as long as it is 99% trichlor, it won't add too much CYA like those cheap Walmart pucks. I rolled my eyes.

My CYA level is currently at 60. I used Trichlor exclusively for my chlorine for the first year I had the pool. Now I only use them when I will be out of town. I plan to do a slight drain/fill later this summer when we will want to add cold water anyway, hoping to get it down to 40 and keep it there. I really wanted to know what to expect for CYA on a per-puck basis, so THANKS!!

If you're going to use Trichlor, and there's no reason not to as long as you monitor pH and CYA levels (pH daily, CYA weekly), you should never, ever use ANYTHING but the 99% trichlor tabs.

For every 10ppm of FC, trichlor adds 6ppm of CYA. That's just a fixed ratio of the chemical and the pool store guy doesn't have a clue.