RO water dude. as long as you use tap, you will never get your nitrates down, ever.
use RO salt for water changes and RO fresh for top off.
you can use distilled in a pinch.
don't do it. i had one tube of an overflow like that fail. water level in the tank rose and spilled over.
dripped on to a sterlizer power brick under the tank and started an electrical fire. luckily a friend was there watching the house or i would have lost everything.
here's what i did. sold...
