Chlorine development in my tank after 3 months!

[808to503]

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Help! I’m stumped. I set up a 5 gallon glass tank 3 months ago, using distilled water and Instant Ocean to a SG of 1.010. Added black sand, lava rock, maple rock, sea fan coral, and other white coral (none live), all from aquarium supply stores. All were boiled first. My water parameters were great (chlorine: 0, pH: 7.25-7.5, hardness >425, Alk: 100-180), temp: 76-78 F. Tank did not truly cycle w/o shrimp. Added 5 opae’ula 2 weeks in, and they did great. Four weeks in, added ~170 opae’ula. Water readings still great. Only change to tank since then has been feeding spirulina powder or Omega One mini veggie pellets occasionally. Topped off tank evaporation with distilled water. Fast forward to recent water parameters, about a month after adding shrimp load, I have chlorine in my water! It’s measured between 0.5-2 mg/L. I do not have a way to measure chloramine, but I assume that’s present as well.
I have tested the distilled water, and it is clear. I’ve had nitrites and nitrates go up, which is understandable, but why am I getting chlorine readings? I have lost a total of 6 shrimp since the the start, which I think is pretty good, but does anyone have any idea how I’m getting chlorine in my water? I am slowly bringing my readings down to acceptable levels using Seachem Prime.
I’m using new test strips, and my fresh water tanks read as expected, so I feel as though I have decent controls in the test strips.
Anyone experience similar chlorine issues? I’m open to troubleshooting opinions.

[Varanus]

I've heard the test strips can be unreliable (the droplet tests are better), so perhaps it's a false positive? In either event, a water conditioner like Prime that detoxifies chlorine should be safe to add to the tank just in case.

[Dch48]

That's strange, I have never heard of chlorine being in a tank without it being introduced by untreated tap water, bleach, or some kind of cleaning product.

Then again, I have never tested for it.

[marianne]

That's strange, I have never heard of chlorine being in a tank without it being introduced by untreated tap water, bleach, or some kind of cleaning product.

808to503, maybe cleaning agents (especially in spray form) used close to the tank ? Or on your hands then touching the water ?
Otherwise, I'd favor the hypothesis of false positive by the test strip

[ShrimpyShrimpShrimp]

Coming from the pool maintenance world i say that this is impossible, baring someone actually putting chlorine in the tank. Test trips are notoriously bad at detecting proper amounts of anything. If you really want to test for chlorine you'll need an FAS-DPD chlorine test kit. Here is some info on that https://www.troublefreepool.com/blog/20 ... rine-test/

[808to503]

Thank you everyone. I know, it's a crazy mystery. I've been very careful and I have not exposed the tank to any chemicals, cleaners, or otherwise. And I know test strips are known to be unreliable, but these are new, and have reflected accurate results in different tanks (both fresh and brackish). I have used Prime to dechlorinate and now my numbers are all to normal acceptable levels, yes, even with the same test strips. I appreciate your input and will just have to remember that periodic testing is something I need to do to keep on top of my tanks.