I have a fully cycled (0 ammonia, 0 nitrite, minimal nitrate) 20 gal tank with 8 platies, 8 neon tetras, 3 zebra danios, and a bushynose pleco. The only issue I have is with the city water supply being very soft and thus acidic. Measuring the KH and GH I get 17.9ppm for each (both turn to their end-colour after the first drop using AP inc test kits). The acidity reads somewhere down around 6.4. The lack of salts in the water doesn't surprise me as most of our water (in the Cayman Islands) comes from either RO seawater or rainwater. My question is should I leave things as is or should I get something like crushed coral to try and buffer the pH up to something more around 7?