The other high concentrations in the tapwater are sulfate at 132ppm, sodium at 21ppm, and chloride at 19ppm. Wouldn't removing traces with carbon negate the point of using tapwater?

Another thought - I'm using Discus Buffer which is monosodium phosphate for phosphate. Is it possible that it is complexing with other things in the water in a way that makes it show up on the test kit but not be available to the plants? The reason I ask is that green dust algae is prevalent and some folks have luck getting rid of it with elevated phosphates. (With this latest dilution though, even the GDA is hurting.)

I see this assertion made quite frequently. However, I've looked all over for references to data showing that activated carbon materially impacts trace levels in actual planted aquariums, and I haven't found any. My limited understanding is that acticated carbon has the highest affinity for adsorbing organic and high molecular weight inorganic compounds, like mercury. Still, I have heard of many aquarists who report using carbon part or full time with no difficulty maintaining thriving planted tanks.

I believe that many municipal water treatment systems already use carbon in the filtration process, prior to disinfection and the addition of other compounds such as flouride.

I had much better success with Austin water, so I looked at the Austin water report again and was surprised to see that they actually invert the Ca:Mg ratio. (The blue boxed vertical column is for the Davis Water Treatment Plant, after treatment.)



If I do another 50% dilution I'll be at about 10ppm Ca and 6ppm Mg.