anyone using ro water in their dirt tank??

i use a mix of tap and r/o to get the ph to ~7.4. the water here is also very hard, so the r/o helps alot

I use RO but I re mineralize it to an acceptable level.

John, we have the same water.
Try aerating it first....not to drive CO2 out of it....but to drive CO2 into it
that will precipitate the hydrated lime.
Then my water settles down to a mid GH low KH and pH around 7.8.
Watch it though, you won't have enough buffer after that so you need to add a little Arm and Hammer back to it.
I use those Rubbermaid cattle watering troughs and hold water for a week.

I'd recommend against using pure RO water in a tank. Much like you, I'm stuck with lousy tap water with a pH of about 8.3 out of the tap and extreme hardness. I tried pure RO in my current planted nano and had wicked pH spikes until I switched to a ~10% tap water/90% RO mixture. Gotta have that buffering capacity.