Chlorine levels spike days after treatment

[donny5]

I'm still trying to wrap my head around this - I treat for chlorine and it tests fine, but days later, no water change, no ammonia spike, yet chlorine levels start to climb again. Is it necessary to regularly treat for chlorine even after the initial treatment?

[saltWaterFreak]

Just to clarify, you're talking about chlorine, right? I've got a pretty comprehensive test kit, and I'm not aware of it having a specific test for that.

[coltin]

Unless someone's topping off the tank with untreated tap water, I'm not seeing how chlorine levels would spike after a water change with dechlorinated water.

[donny5]

I'd say it's possible the chlorine level is rising due to a few factors. Firstly, some test kits might not be entirely accurate, so it's worth double-checking with a different kit. Secondly, if you're using a dechlorinator that's not very effective, it might not be removing all the chlorine from the water. Lastly, it's also possible that there's a bit of chlorine being produced naturally within the tank itself.

[donny5]

Unless someone's topping off the tank with untreated tap water, I'm not seeing how chlorine levels would spike after a water change with dechlorinated water.

That's what's got me stumped - nothing's being added.

[coltin]

I've been wondering if the issue might be with the test kit itself.
Is it a liquid or paper test kit you're using?
Also, when's the expiry date on the kit - is it still in date?
And just to cover all bases, are you storing the test kit in a cool, dark place?

[donny5]

My test kit's got paper tabs, bunch of 'em. Don't have chlorine in the API test tube kit though.

[bettaMagenta]

I'm on the same page as coltin, a faulty test strip seems like the most plausible explanation here. It just doesn't make sense for chlorine levels to spike out of nowhere without any new water being added. Now, I'm left wondering which test result is the accurate one - the initial zero reading or the later positive one? I always try to verify weird test results, but sometimes you just don't have multiple tests to fall back on. Did you happen to use multiple strips that all showed a positive reading?

To me, false positives seem more likely, since chlorine should naturally dissipate over time with decent circulation or aeration in the tank.

[sidthy]

I'm wondering what dechlorinator you're using - some of the older ones might not be effective against chloramine. Chloramine can break down into ammonia, which would get filtered out, and chlorine, which could be causing your readings.