COVID AND THE VACCINE - TRUTH, LIES, AND MISCONCEPTIONS REVEALED, page-29625

The only thing is RO Reverse osmosis water, regarding fish is there are no mineral buffers to stabilize the waters ph (i.e cal/mag) to stabilize PH so you can have deep swings in PH with RO water, if you cycle your tank with a bit of substrate or seachem matrix at the bottom of the drum, say a liter, over time your ph will stabilize. But i guess your hydroton / perlite with become your substrate , although you did state the system is separate , so you will still need to cycle the fish part utilizing some media to grow the beneficial bacteria, bb. I guessing you know about cycling a tank before adding fish?

Ammonia-Nitrite-Nitrate process

I recommend not trying to adjust PH for the plants too much or for the fish , a stable PH decline over time is better than one that swings, both plants and fish are adaptable to PH gradual movements, but it is the rapid swing that harm or kill them. So If you PH if 7.5-8 from the tap it will natural fall over time, at 6.2 you can replace so water to lift PH, changing out a bit of water if better than using PH up buffers. AS for the EC/CF of the concentration of nutrients, for your plants , less is often more, don't over do it. Bluelab PH or EC pens are good.