How to lower Ph of rockwool cube?

I need to lower the Ph of my rockwool cubes. I do not grow hydro. I just pour water into the cubes 2x a day.

So can I just create a couple gallons of water at ~6.0ph and water with it to lower the Ph?
Can I use Ph down solution that is suppose to be used in aquariums? Or is that not safe.

Any advise is appreciated.
Thanks

that should work - keep in mind you probably want to ph your water a point or 2 lower than your target ph. (so 6.0 should totally work), unless your rw ph is something ridonk, which i doubt.
as far as using aquarium ph down, i don't know anything about that, but i would assume that if it's safe for your fish to swim in, it's probably safe to water your plants with.