m0useanswered grow question 5 hours ago Flushing is mostly a myth and distilled water is aggressive as fuck and could burn the roots. Almost any acid can be used as a PH down. citric is not outside of the realms of common acids used. I think GH PH down has a mix of citric and phosphoric.
Flushing is just not needed, it does not do most of what people claim it does, like removing chemical taste from buds, it's just not how plants work..
It is however a useful tool to combat toxicity of the medium should you have accidentally overfed it to much.
In short feed less and then just water as needed end of life vs dumping copious amount of water though the pot. Agree with others, distilled/RO is just wasted money and not needed.
Good Luck!