copper MUST be zero (0) in a reef system, there is no exception. and once copper has tainted a system, its almost impossible to get out. so as far as your reef system goes, it has to be drained, cleaned, all of the contaminated rocks/sand/rubble are to be throw out. any filters in the reef system should also be tossed. b/c you will never get that copper out of the system.
be sure to check the copper levels in the fish system, b/c if they are zero (O), you may be able to switch which systems are reef and fish.
low levels of copper are "ok" in your fish only systems, b/c allot of medications contain small amounts of copper. but you still have to do regularly scheduled water changes to keep those levels in check.
as far as the fish only system, 5ppm of phosphates is unacceptable. thats higher than some tap water i've tested. getting phosphates down is going to be a losing battle unless you can identify where the phosphates are coming from. its most likely poor DI water quality, and the rocks. so again, i'd toss the rocks out, drain the tanks, clean and disinfect. then make sure to get new DI tanks and make sure your conductivity is below 10 (like Nbmaxx suggested)
phosphates and copper are very hard to rid of. it will be a losing battle to keep these systems running and try to use chemicals to neutralize these things. in fact, the more chemicals you add to correct for other things, the worse you are probably making things as allot of chemicals also contain phosphates.