Testing Tri-chlor tab effectiveness

[ezpool]

I have a large bucket of 3" Tri-chlor tablets that I've been using in the pool. I have no idea how old they are - we got them and the pool from the previous home-owner. I've been using them but I've also had to add bleach almost nightly to maintain a free chlorine residual (even though the tab floater is set to max). Today I decided to try to determine if the Tri-chlor tabs are actually doing anything so I dropped half a tab into a cup of water and let it sit. About 9 hour later I tested the water with my Taylor DPD test kit and got some really weird results:

- Added 5 drops of R-0001. No color change, none expected.
- Added 5 drops of R-0002. Each drop turned pink as soon as
it hit the water but then immediately faded to clear. After
swirling, the solution was still completely clear.
- Added 5 drops of R-0003. The entire solution turned a very
very dark murky brown.

There was definitely a smell of chlorine so I think the tabs must be somewhat effective but the above results have me scratching my head. Would this be expected if there was much more chlorine in the water that the test was meant to measure?? Or if the tabs are bad?

Thanks in advance!

[aylad]

Don't know about your test results, but your chlorine demand may not be because of the old tabs--you don't post readings for FC and CC, or for CYA. I suspect that if you are running your trichlor feeder wide open, then your CYA may be very high, high enough that the tabs can't provide adequate chlorine. If you'll post current numbers for FC, CC, and CYA, it would help us figure it out...

Janet

[DavidD]

...I dropped half a tab into a cup of water and let it sit. About 9 hour later I tested the water with my Taylor DPD test kit and got some really weird results:

- Added 5 drops of R-0001. No color change, none expected.
- Added 5 drops of R-0002. Each drop turned pink as soon as
it hit the water but then immediately faded to clear. After
swirling, the solution was still completely clear.
- Added 5 drops of R-0003. The entire solution turned a very
very dark murky brown.

There was definitely a smell of chlorine so I think the tabs must be somewhat effective but the above results have me scratching my head. Would this be expected if there was much more chlorine in the water that the test was meant to measure?? Or if the tabs are bad?

First of all, if you dropped a half a tab in a cup of water and let it dissolve, your FC would be a gazillion ppm (not really, but really really high) and your PH would be around 2. You are using DPD testing which is only good up to 10 ppm of FC if I'm not mistaken (FAS-DPD powder test to 50 ppm if memory serves me correct). So your results aren't any good I'm sorry to say. The combination of extra high FC, your testing method being out of range with the low PH is bleaching the pink right out.

I would continue to use them in the pool and post some numbers like Janet suggested. That way you are actually seeing what is happening in the proper volumes and PH range.

Dave

[duraleigh]

You probably had well over 10000ppm. On the bright side, you shouldn't have any algae problems in that cup!!

[DavidD]

Well, on the bright side, you shouldn't have any algae problems in that cup!!

Never thought of that!

Dave

[ezpool]

Hehe, the cup *was* very clean afterwards. My main reason for posting was to try to figure out if I should toss these tabs in the trash or keep using them. From the replies so far, I guess the tabs might still be good. My numbers have been mostly fine: FC 2-3, CC 0, pH 7.5, CH 250, CYA <30

My confusion is based on two things:
1. Even with the floater wide open I still need to add bleach to keep the FC above 0.
2. My CYA level has never risen even though I've been using tabs since opening the pool (it was 0 initially until I manually added a few pounds of CYA when it became clear that the tabs weren't doing the trick).

My original intent was to just use the tabs until CYA gets higher and then switch to bleach only. But this hasn't happened... Anyone know how much CYA is actually in these tabs (Leslie's brand)? I.e. is there anything that says "using XX tabs will add YY ppm CYA to a 10K gal pool"?