City water vs whole house filtered
 

Everything is in place to start adding water to a new aquarium. Since my last hobby aquarium was dismantled in 1975, I have been reading 100's of posts on this site, and I now have all the information, knowledge and skill to insure success (HAH!!!)

In my reading, I've not come across this question, so I pose it now...
My city water is hard and we have a whole house filtration system, both carbon and salt. In addition, there is an undersink RO system. So, when I fill the tank initially, what water should I use? And when I do regular water changes? I'm guessing start with a mix and see what the numbers are in a couple days, but I'd rather hear from someone in a similar situation.

Is there an advantage to one or the other; more importantly is one or the other more likely to cause problems?

Thanks,

You do not want to use post softened water, the added salts will not be good for the fish.

What you do will ultimately depend on what fish you intend to keep. With hard water fish, you'll just use pre-softened water right out of the source. Add some dechlorinator and you're done.

If you want soft water fish, you'll need to mix pre-softened water with the RO water to get the desired hardness. You can replace the RO water with rainwater if you wish.

For either case, that will be your routine for every weekly water change. Either 100% pre-softened, or the same mixture of pre-softened and RO.

I personally used soften water for years and never had an issue with the traces of salt it added to the water. Though I did have to start dosing magnesium sulfate to my high tech planted tanks as the softener stripped it all out and lead to some deficiencies in my stem plants. As far as the fish are concerned the softener does not really soften the water. The total dissolved solids are unchanged for the most part. I have spawned or raised a lot of community fish in softened water so I really don't think its an issue.

You can certainly use pre-softened water if its available to you, but from my experience at least if its a full house system its a pain to get pre-softened water. Your only option will be cold water. I perferred to just go with the softened water.

I'd suggest you use either the raw supply water OR the RO water but the RO water will need to be treated with mineral additive and/or pH adjuster. I use a mix of filtered 'tap' water and deionized (DI) water (from an API Tap Water Filter). I use Seachem Replenish and Seachem Neutral Regulator and Seachem Alkaline Regular.
I also add Seachem Fresh Trace during weekly water changes. I've been doing this for four months to combat high nitrates in my well water - working well so far.

AbbeysDad what do you think about this:

If half R.O. and half hard tap water was used would it not create a good mixture of water. The hard water with the R.O. water. This is basically what I am doing. That way no extra chemicals need to be added?

You would have to test the water after mixing it though? hmmm.

Yes, that works well.

I believe Abbey avoids the raw well water because of extreme Nitrate levels.

As has been mentioned, we need the numbers for the GH, KH and pH from the tap water (both pre and post softener), then we need to know the intended fish. I agree with the easiest approach, and this data will help us achieve that.

Thanks to all who have replied with suggestions. I'm waiting for the FedEx truck with my filter and other supplies (Wednesday?) and am hoping to determine best approach to filling tank initially. When I get the test kit, I'll see what my water parameters are an post them.

Yes, that could work fine...and yes, I have a problem with very high nitrates in my well water (the result of a 95 acre farmers field across the road). I setup a 10g in the garage and use either Fluval Nitrate Remover (FNR) or API Nitra-Zorb to remove nitrates from the well water. I've been mixing this 50/50 with deionized (DI) water from the API Tap water filter. I treat the DI water for pH and minerals as I'm not looking to alter water chemistry (e.g. make my water softer) but rather add/use water for water changes that is "community tank friendly". Because of this extra effort and cost of water, I reduced water changes to 10g weekly on my 60g tank. This is actually on the low side so I stepped up water filtration/purification. In addition to several bunches of floating Anacharis plants, I periodically use products like activated carbon, Seachem Purigen, API Nitra-Zorb in addition to my DIY bio-filter canister filled with nearly 4 liters of Seachem Matrix & De*Nitrate media. (I also have some API Bio-Chem Zorb to try at some point).

Note: Prior to the discovery of high nitrates in my well water, I had a lot of unexplained fish loss - especially Platy fry that just didn't make it past few months. Since addressing the nitrate issue per above, I haven't lost a fish and the fish, including the fry, are vibrant and growing.

I will be adding more living plants in the future to further combat tank generated nitrates.