My main display tank is a former freshwater planted tank and I used a number of treatments in the tank that included copper over time. I now have been running it as marine for 3 years and have had a number of inverts over the years including currently a coral banded shrimp that has been in there for 2 years, glass/anemone shrimp, hermit crabs and thousands of worms. The tank is also linked (with a common sump) to my mantis shrimp tank and all of the inhabitants are fine. I dont think the copper leaching out of silicone thing is as bad as people think, plenty of people top off with tap water which comes through at least some copper/brass pipes and therefore contains some dissolved copper.
Copper is toxic to (almost) all living things, the trick is the dose, I think the copper is in such a low concentration that microbes etc. will break it down to an insoluble form before it becomes a problem.
Also I read about a treatment to remove almost all traces of copper from a tank using just bleach or ammonia and vinegar, I think... It was a while ago!