Hello all,
I may have finally found the source of heavy metals. I just realized it this morning when I was cleaning my sump. I have a large filter sock that appears to have a metal, not plastic ring. The ring is soldered together and I've been using this filter sock for months. I assumed that the ring was a heavy duty plastic but I was wrong. The filter sock recently started showing rust stains. I hadn't even noticed that.
I bought the sock from dudadeisel.com. It is a 600 micron sock and isn't one that is typically used in an aquarium.
According to reference. com, s
older alloys are made from a mixture of tin, lead, brass and silver. Solder made from tin and lead has a lower melting point, while brass and silver are used to create an alloy able to withstand higher temperatures. This metal ring hidden inside the cloth liner is making the cloth rusty right at the point where the ring is soldered together.
Wikipedia states "
solder should also be resistant to oxidative and corrosive effects that would degrade the joint over time."