Recently installed an RO unit under the sink - sick of to-ing and fro-ing between the LFS and my house especially now that my Bolivians are regularly spawning I have a need of more RO water for fry tanks.
The unit is giving me RO with a TDS of 10, pre-filtered water is measuring 380-405 TDS, with a GH of 18-odd. I am not using a DI to get it right down to 0, I think that would be overkill.
I mix it with tap water to get a kh of 5, gh of 8, ph 7.4 (using API test kits), but I'm wondering what sort of minerals I could buy instead to re-mineralise the water - and whether it would actually be worthwhile? I assume something branded for use with Discus would be the right sort of product?
If you're not keeping very sensitive fish, a mix with tap water will do the job just fine.
If you want to remineralise, you can go for a species type mix as you've mentioned or you can use somethning like Seachem Equilibium (a powder remineraliser which aims to also help plants) or Replenish (which is a liquid). With these products you can target a specific gH, but will need to adjust kH and pH as well as they don't add any alkalinity.
How rude of me not to thank you both for your suggestions.
I haven't yet made the move to adding minerals but I am thinking of trying the equilibrium product first. I'm fed up with having buckets of tap water hanging around for 24 hours+ prior to water changes.