If your copper levels are too high for Prime, Seachem also makes Seachem. CupriSorb
If you want to do RO
, mix a rinsed, measured amount of crushed oyster shells (huge bags available at feed stores for chickens) into a measured amount of RO
, leave it a week, then test kH
and adjust from there so you can math out how much you'd need to get your whole tank to your target numbers. It sounds kind of OMG no, but once it's sorted out, it's easy to measure out for future changes. There's other stuff you can use, but crushed shells will address both kH
where most other options require more steps and are more expensive.