should I get RO water?

[zlk718]

I live in Arizona where the water is very hard. Is it worth using remineralized RO water or a mix of RO/tap water if I'm planning to keep fish like tetras? If so how do I find out what mix to use? My other question is about fertilizer. With very hard water should I be dosing much less fertilizer than someone with very soft water? Its unclear to me whether some or all of the minerals contained in fertilizers are already present in my water. Like I assume something such as easy iron would do more harm to my plants than good? 

[JettsPapa]

What kind of tetras do you want?  Serpae tetras, pristella tetras, black neon tetras, and lemon tetras are all doing just fine in my water, and my daughter-in-law successfully kept Congo tetras and diamond tetras.  Her water comes from the same well mine does.  The AC test strips show both my GH and KH at around 300, and my pH is 8.2.

[Kurt Brutting]

I cut my tap water with RO water 50/50 to get the parameters I want. If you want to use RO with tap water you need to experiment. Use buckets or cups and test, test, test. Once it’s in your aquarium with fish & plants you need to keep an eye on your parameters because it could change once cycled or settled. I dose seachem equilibrium in the RO water for minerals. I use an electronic scale to measure the amount of equilibrium I am adding. 

[Kurt Brutting]

With that said most fish will adjust to most tap water. I kept Cardinal & Buenos Aires Tetras in very hard water with high PH.