[Water troubles]

Thanks everyone for the advice. Sounds like I was just overthinking things. All the care guides I read on neons and corys said they prefer soft and slightly acidic water. I’m a bit of a perfectionist so I was trying to get to those ideal conditions. I’ll do the crushed coral and ditch the RO and stick with tap. Thanks again. 

[Water troubles]

So, I'm new to the hobby but I've been researching quite a bit. I'm building a 29 gal. Sand, dragon rock, driftwood, and planted with java fern and anubias (16 plants total), as well as java moss and guppy grass. I intend to keep cherry shrimp (already have 30+ in a smaller tank), 10-12 neon tetras, 6 pygmy corys, a clown pleco, and 3-4 nerites. The tank is already cycled and planted but no livestock yet. Keeping temp at 78 and running Aquarium co-op's sponge filter. My issue has been water parameters. I started out just using tap. Out of the tap, it runs 6dKH, 8dGH, and pH 7.8-8.0. I wanted to lower my pH so I got the Buddy+ RODI kit and started doing 30% water changes every week while it was cycling. Apparently I did one too many because my pH crashed down to 6.2. I've managed to get it back up to 6.8-7.0 by doing mixed water changes with RO and tap. My concern is my kH. Current water conditions are pH 7.0, 7 dGH, and 2 dKH. (Aslo, 0 NH3, 0 nitrites, 20 ppm nitrates - adding NH4CI daily until stocked) I tried adding some sodium carbonate in the form of API's pH UP, and that got my pH up to 7 but had no affect on my KH. I'm worried about my plants and pH swings with that low of KH. Am I right to be concerned and if so what should I try differently?