I keep them just fine (they even berry up) in soft water at around 74F-78F in my 20L with nothing more than an Eheim 2217 with an in-line atomizer for CO2 and a Vuppa for surface skimming. However, my tank is extremely dense with plants. I'd like to think that oxygenation plays the largest part in keeping amanos alive in a CO2 injected setup. Lots of plant density + no surface film = lots of oxygen. If your amanos have a bluish hue to their innards when you find them dead...too little oxygenation. However, that is a really low TDS so you may want to up the gh a tad bit.