Originally Posted by imcosmokramer
I use RO/DI water because I already have it for my reef tanks. Is there a reason not to use it? Wouldn't it have chlorine in it? and nitrates? (at least that is why we do that in SW).
By hardness, are you guys talking about alkalinity? Sorry for to basic questions, I just know nothing :)
If you ever have any saltwater questions, I'm your guy.
Izzy has answered your questions. With freshwater, minerals in the water are needed by some fish (such as guppies or any livebearer), less by others (very soft water fish). Your tap water will have some degree of hardness (GH) caused by some of these minerals, mainly calcium and magnesium. Depending what level of hardness is in the tap water, for livebearers it may be better than RO which of course removes everything.
We in freshwater like to do regular weekly water changes. If one is able to use the tap water, this is much less trouble. Water conditioners detoxify chlorine, chloramine, most also heavy metals. Knowing your tap water parameters (GH, Alkalinity, pH) is essential.