What is your ph? 300ppms is high for neons. Mine is naturally a little higher than that, and I had bad luck with tetras before I started using RO. Pillows work too, but they aren't much fun to keep. You have to keep recharging them and what not, its easier (but a lot more cumbersome) to use RO. I can now keep all kinds of tetras, rams, gouramis, and other fish known to love soft water with my RO.