View Full Version : How to Tell if Chlorine Tablets Bad (Exceeded Shelf Life)?

02/26/2015, 04:49 PM
If test sample turns dark pink/red coming off of a brand new carbon filter in the RO/DI system, could that indicate bad Cl tablets (e.g., exceeded shelf life)? I just replaced carbon block because previous sample went dark pink/red like that, but sample taken just after replacing the carbon block (and running water through it for a couple minutes) also went dark pink/red very quickly, i.e., as soon as I swirled the sample. I am hoping it is bad tablets and not bad replacement carbon block.

I read that the Cl tablets have a three-year shelf life, and it is quite possible mine were at that. However, the place I read that further indicated that the tablets would either crumble or discolor if they had gone bad, but mine looked normal (white, intact). The blisters the tablets were in were intact, but things do degrade over time.


03/23/2015, 10:12 AM
It could.
It could also indicate your filter is bypassing, insufficient rinse up, or that you are exceeding the contact time required with the load of Chlorine/mines in your water source (it may have changed too).
Before jumping off into could be's, have you tested previously after carbon change and has there previously been a not detected color indication after filter change, or is this a new indication?


04/27/2015, 11:03 AM
I posted the question after replacing with a carbon block that was not from SP. Assuming it was the tablets that were bad, I got new tablets, but still had chlorine showing up. So I figured it was the carbon block. The gaskets looked thin and not pliable, so I think the filter did not fit the canister/housing properly. Therefore, I replaced with an SP carbon filter. Unfortunately, STILL had chlorine showing up. Solution was to put a second carbon block in line with the first carbon block, and now water shows no red/pink at all coming off the carbon blocks.

04/27/2015, 03:11 PM
What is your incoming ppm of chlorine? Did you rinse the vial out very well when running the second test. This is the first time I have heard of our carbon block passing through chlorine. I have tested hundreds and have not seen that. Do the gaskets have bite marks on them? What micron rating did you get?


05/01/2015, 08:43 AM
Not sure what incoming is, but if memory serves me it went pretty dark red.

Yes, I washed vial using the waste effluent from RO, which came up clear. (While trouble-shooting to see if the tablets were bad, I tested that.)

Carbon block is 0.5 micron.

I think I've always seen a bare tinge of pink off the carbon and just assumed the tablets would impart slight, slight coloration; I would replace when it got dark enough to reach the first numerical value on the color chart. It wasn't until putting second carbon block in tandem with the first that I see treu clear going into the RO membranes.

No worries here, I'm pleased with the setup

05/01/2015, 08:47 AM
I have operated commercial swimming pools for years and can tell you CL test tabs go bad, most of the time they do not crumble they just give you bad readings.

05/06/2015, 09:55 AM
Thanks for chiming in Timmy! =)