I personally wouldn't worry about copper levels from pipes and tanks, they will be minimal at best and with 50% water changes per week that dilutes what is already a tiny, tiny amount even further. Prior to coming back to freshwater I kept marines for over 10 years culminating on a 1000 litre full SPS reef system. Corals are particularly sensitive to copper but I didn't see anything that indicate there was an issue. There were also marine shrimps in the tank. We were living in a 1950's build property at the time