I have tried Tonina in harder water KH 7 GH 3-5 on three different occasions with not much luck. All other plants were growing just fine.
At the time I was growing plants like Stargrass, Pearlweed, Eriocaulon's, Ludwigia cuba, HC, Downoi, R. macrandra, but I just couldn't keep the Toninas alive. The Tonina would hang on for about a month to a month and a half and then just start turning brown and waste away to nothing.
Maybe you can tell if you see something wrong with my fert regime.
30 gallon, 3.6wpg PC, 10ppm KNO3, .73ppm PO4 every other day and on the other days I add 7.5ml of Flourish and 5ml of Flourish iron. 50% water change on Saturdays. CO2 kept at 30ppm with a controller.
Like I said everything else grew just fine and is still growing just fine.
I have grown Egeria najas in the past but didn't like the intense growth.
Like I said though this is basically an experiment. I have been hearing you in the past putting down the need for soft water with some plants and I thought since the harder water wasn't working so good for me I would see what happened with the soft water. Believe me I tried my best to put this "myth" to rest myself and just couldn't. Now I want to see what will happen with the soft water.