So I've been setting up a mini pond this summer for the first time and I've had one set up since 4/21/22. I always dechlorinated the water when I topped off but I was getting really thrown off by these chlorine readings I was getting on the test strips. It seems like I would still get chlorine even when I hadn't topped off with any water but rain water in weeks. After searching the forum for people running into similar issues, I initially thought the container I was using (a resin planted from Home Depot) was leaching chlorine. So I completely changed over the substrate, sponge filter, and plants to a new container which was actually a used black water trough container I bought from someone who had used it heavily for farm animals.
After filling the new container up and dechlorinating, I took a reading and again a high amount of chlorine. I dechlorinated a second time and tested again the next day, again more chlorine. I finally realized that both containers could not be leaching chlorine. So, today I performed the following test and got some surprising results.
I did the following:
1) Dipped the test strip into the dechlorinated pond and took it inside immediately for reading
2) Took a water sample from the dechlorinated pond inside and then dipped the test strip in it
3) Dipped the test strip into the dechlorinated pond and left it outside in full view of the sun
My results were as follows (see attached image)
1) No chlorine
2) No chlorine
3) At least 3.0 ppm chlorine
The experiment wasn't perfect but the only variable I changed was the sun exposure on the test strip. I wanted to test my inside tap water to see if the sun was really causing these high chlorine readings. So I dipped a new test strip into a sample of my inside tap water (dechlorinated) and then put it outside in full view of the sun before I read it. I ended up getting more than 3.0 ppm chlorine.
I wasn't aware that UV light or the sun would effect test strips like this and a lot of other kits don't even include chlorine so I thought this was interesting to share. Especially with so many of us setting up summer tubs right now!