I kept and bred tetras, Cardinals and Rummy Noses, in SB which has worst(harderwater) tap than LA(KH 9, GH 24). Tap pH doesn't mean a whole lot for a CO2 enriched tank.
If I can bred them, I think the hardness while it may improve fry yields, is not as big of a key as folks like to think.
Food, O2, good stocking level etc are the prime important factors. Total salt content is more important than pH for just about all fish. pH moves around and is influenced by many things in nature and in out tanks. If you wish to bred Apisto's, raise wild stock etc, you might want to blend with RO, at least you drink the RO, try that using peat water
But the peat and softer water does not help the plants. It's only for a few fish species/breeding
Regards,
Tom Barr