I would say there are many aspects to be considered before using RO, which is expensive and not that easy as using tap water. The question would be: how's your tap water? Any areference analysis? How many liters per week do you need? Can you harvest rainwater? Is your first planted tank or do you have some experience? Which plants do you want to use? Do you want to breed soft water fish?Hi guys Should I be using ro or tap water to first fill my new tank.
Exactly the same for me in the Spanish Eastern coast... liquid rock. I tried a few months ago for the first time the 60/40 tap/rainwater mix and I am very happy with the results (I have just shrimps for the moment, but very good results with plants also). I just buy RO when I run out of rainwater but to be honest I have only small tanks (total volume, barely 85 liters) and for weekly WCs I use about 15 liters of RO/rainwater (and the cistern where I harvest the rainwater has 1,200 liters!)f you're in East Anglia,like me,then it will be rock hard,high tds and high ph which is no problem for most plants but for Tetra then not so good.
I currently do a 60/40 rainwater/tapwater mix or if I run out of rainwater then I use RO which brings it down to somewhere near reasonable levels but I'm not keeping Tetra who would probably appreciate it softer than that.