Soft Water Breeders (GH 0-4, KH 0-2)
Wild betta species, cardinal tetra, rummy nose tetra, German blue ram, discus.
Reverse osmosis water remineralized minimally with Seachem Equilibrium or similar.
pH typically 5.5 to 6.5.
Medium Water Breeders (GH 6-10, KH 3-5)
Angelfish, corydoras, rainbowfish, most gourami species, zebra danio.
Tap water is often usable with simple dechlorinator.
pH 6.8 to 7.4.
Hard Water Breeders (GH 12-20, KH 6-10)
African rift lake cichlids (mbuna, peacocks), livebearers (guppies, platies, mollies), goldfish.
Crushed coral in filter or substrate maintains parameters.
pH 7.8 to 8.4.
Adjusting Source Water
Soften hard tap water with RO dilution (50/50 or more).
Harden soft tap water with aragonite, crushed coral, or commercial mineralizers.