It's possible that jebao pump releases tin. A quotation from another forum: "It's relatively low maintainence, I only have to change out the dosing solutions once a month-ish and add a few drops of nutrients whenever I feed the fish. I rarely do water changes unless something seems off, which at one point, it did, as a Jebao pump was rusting in my sump leeching tin into the water. It's since been replaced and the tin has dropped about 60%, slowly getting back to zero."
Read also
https://www.reef2rainforest.com/2016...f-being-cheap/
Krzysztof