"Ben" wrote in message ...
The key here is that my tank is a FULLY planted DISCUS tank.

I've had Discus in KH of 5/GH 9 tap water, things breed, fish are
fine. Temp's 82F.
If the tap is real hard(6-8KH and 10+ GH) and if breeding is a real
concern etc, RO should likely be used.
If neither the tap nor the breeding issues are a real concern, the
answer would be a resounding "no".
RO is not needed if you have moderately soft tap water(like the above
water I had). If all you want to do is breed Discus and feed them as
much as they can eat , then do that, have barebottom tanks etc/large
daily water changes etc.
If your goal is both, follow the advice that's be given. KH-3-5, GH
3-10.

Regards,
Tom Barr