Hello,
substrate for plants can stabilize pH around 6,5 or 7. I only use a thin layer of sand and if it must be clay balls (for Echinodorus in pot). Experiments with thick layer lava granulate went wrong (pH around 7). With sand-substrate, peat and pure RO water pH easily drops down under 5. Avoid carbonate hardiness, with KH the pH will not drop down and the Paros eggs can not exist.1/4 tap water means more than KH 2 and this result in pH higher than 7! And in my opinion you do not need aqua safe or other related products, because RO-water or rainwater is pure water without copper or other harmful metals/substances.
Greetings Patrick