Epsom salts (magnesium sulfate) raise the magnesium level slightly. The increased sulfate levels effects are unknown, but the use of epsom salts has been around for ages and is considered very safe.
I wouldn't use GC in the water column of a display tank. We do use it mixed with food and Focus to treat fish in the DT, but feed carefully and remove any remaining mix. The problem is you don't want the organisms to build up an immunity to either of the components (praziquantel and metro) so the drugs end up being useless when you need them. Might be why we are seeing prazi resistant flukes these days. The LFS or shippers may be dosing sub therapeutic levels of GC to keep fish "sellable." As they are known to be doing with copper. And that has caused a huge problem as fish suddenly break out with awful velvet and ich infestations when the fish are sold and released into unmedicated/untreated tanks in our homes.
I wouldn't use GC in the water column of a display tank. We do use it mixed with food and Focus to treat fish in the DT, but feed carefully and remove any remaining mix. The problem is you don't want the organisms to build up an immunity to either of the components (praziquantel and metro) so the drugs end up being useless when you need them. Might be why we are seeing prazi resistant flukes these days. The LFS or shippers may be dosing sub therapeutic levels of GC to keep fish "sellable." As they are known to be doing with copper. And that has caused a huge problem as fish suddenly break out with awful velvet and ich infestations when the fish are sold and released into unmedicated/untreated tanks in our homes.