Fish require very few trace elements and besides, the majority of their dietary needs are met perfectly well by any of the common flake foods.
If you're trying to address the needs of the fish, the GH isn't all that important. If you do want to supply Ca & Mg, why not use CaSO4 and MgSO4? These compounds dissolve pretty quickly and sulfate is pretty innocuous when it comes to both fish and plants. I'd add a bit of CaCl2, just for the calcum, and maybe a bit of K2SO4 for the K. Flourish trace doesn't add anything that regular Flourish doesn't. It's pretty much a product without a purpose as far as I can tell.
Honestly, if you're not trying to do something special, why not add 10% or 20% tapwater to your RO? That would be 100 times easier than messing with all the chemicals.
Don't forget KH. When it comes to fish, this is far more important than GH.
If you're trying to address the needs of the fish, the GH isn't all that important. If you do want to supply Ca & Mg, why not use CaSO4 and MgSO4? These compounds dissolve pretty quickly and sulfate is pretty innocuous when it comes to both fish and plants. I'd add a bit of CaCl2, just for the calcum, and maybe a bit of K2SO4 for the K. Flourish trace doesn't add anything that regular Flourish doesn't. It's pretty much a product without a purpose as far as I can tell.
Honestly, if you're not trying to do something special, why not add 10% or 20% tapwater to your RO? That would be 100 times easier than messing with all the chemicals.
Don't forget KH. When it comes to fish, this is far more important than GH.