what rugie is saying is to add the RO right, which replenishes desired minerals
i believe just purified water is harmful to fish.
so JUST purified water harmful, not purified mixed with tap, such as water filtered with a Britta filter, or mixing treated water with spring water?
Normally I just only use tap water treated with Jungles start right conditioner. However, the pH is very high, a full point over Betta's max [8.5]. They seem to do fine for awhile, then fin rot starts to show. Ill treat them, it will go away, however, not fully as within a week or two, back again.
I had been doing one weekly flush of 25-40% every week on sat. [prep water Friday], however, mid Dec I increased it to at least 50% water flush, same time a week thinking I wasn't changing enough water.
I have 2 tank setups, one 10 gal where my Betta's live. The other is a larger community tank housed with mostly guppies, and one Chinese algae eater. Was told its a 15 gal, but compared to the 10gal [setup next to it] seems to be more a 20gal.
Both tanks use power filters
tested water both myself and also brought some water to a fish person / shop to double check my numbers, as well as get some advice. He said at the time there were VERY small indications of ammonia, but so small it wouldn't effect their health. The biggest one that was off charts was just the pH at 8.5
just re-checked my Betta tank today[didn't bother with larger tank as today is the flush day for it]
when I added 2.5 gal of spring water to my treated tap water, it brought my pH it a nice 7.6 :D
Nitrate [NO3] is roughly at 5.0 [light orange-yellow]
Nitrite[NO2] is at a nice sky/baby blue 0
Ammonia [NH3/NH4] slightly higher then 0 [not happy face yellow, but also not distinctly neon green], wouldn't say .25, as that'd be too green for match, more about .10 or so. [didn't match the 0 color swatch, but also didn't match any of the green ones either] This matches what the shop person was saying, as he too said there were very small traces of ammonia, but not enough to harm then or cause the rot that's been relapsing.
I also have test strips to show the water hardness etc, but don't like to use them if I don't have to.