Question about tablets

[LeeM2]

I was out of liquid chlorine last week, so I put 5 tablets in 2 floaters, 4 tablets in 1 floater and 1 in the other. CYA 35 allows it.

I had both floaters half open, which kept my chlorine level between at 3-3.5 every single day. We had a couple of rains in the last couple of days (one last night) and now I have about 3-4" of extra water that I didn't have when I put tablets in.

Today, the 7th day, tablets are about 80% dissolved and I still have 3ppm. How is that possible? Does it mean tablets have higher concentration on the inside than on the outside, which allows them to keep chlorine level even when they are 80% dissolved?

Thanks

P.S. I always fight with PH which climbs up all the time, and rain tends to not affect if not raise my PH level. I have my TA between 90-110 and keep adjusting PH to about 7.4 once I see it above 7.8.

I don't know what PH level I had when I put these 5 tablets in, but these tablets kept my PH in range. When I use liquid I adjust PH more than once a week, more like 3 times in 2 weeks. I don't know if these last rains were more acidic than always, but today, on 7th day of using these tablets my PH level is about 7.5.

 

[Richard320]

Trichlor tablets are acidic, which explains why your pH has stayed steady.

The tablets don't hold chlorine, they ARE chlorine. And the more surface area, the faster they dissolve. Check them out - the remnants are rough and cratered, not smooth like they were when they were new.

Them pucks are appealing, no doubt about it. They can make for an almost maintenance-free pool. Until they turn on you.

 

[LeeM2]

Trichlor tablets are acidic, which explains why your pH has stayed steady.

Yes, I think they are ph 3 or less. I would like to know how to make it steady with liquid chlorine. Should I lower my TA a bit?

The tablets don't hold chlorine, they ARE chlorine. And the more surface area, the faster they dissolve. Check them out - the remnants are rough and cratered, not smooth like they were when they were new.

I know, but the question was - how do they manage to hold chlorine level in the pool when they are almost completely dissolved. I had 3ppm today at 8AM and I have 3ppm at 8PM.

But I think I may have the answer to my own question -
We may had sunny days the first few days, when I started using them and they were 8oz each. We haven't had as much sun for the last few days when they got smaller (and were contributing less chlorine), so the chlorine in the pool wasn't used up as much. Unless of course someone knows for a fact that they have higher concentration on the inside than on the outside.

 

[chem geek]

They have the same concentration throughout. I think in your case it's mostly the weather. When I used Trichlor tabs/pucks years ago, I found that when they got fairly small they wouldn't output chlorine fast enough. I added another tablet when the previous one went from 3" diameter to somewhere under 1". This is with the tablet in a floating feeder. The surface area of a smooth tablet decreases as it gets smaller, but as Richard pointed out earlier the surface gets rougher which increases its surface area and these two effects tend to make the dissolving rate roughly constant until the tablets get quite a bit smaller.