My tap water is liquid rock. pH of 8, sky high gh and kh. I have a tank with german Ram fish in which I use 4 parts RO to 1 part tap. It gives me a pH of 7.4 and TDS of 150. Not sure on gh or kh, I have a test kit coming in the mail.
My question is whether I should use a mixture of tap water and RO in my tank, or would it be better for breeding purposes to use RO water and add minerals back in? I've heard OEBTs like a very low kh. If I were to add my own minerals, what would I use?