Join Date: Oct 2007
Location: Ontario, Canada
I use a water softener at home. Not by choice, but happens to be there. I don't have problems growing plants.
The water softener uses salts to "swap" or trade ions with the minerals. So magnesium / calcium ions are swapped for whatever salt you have. Most common salts are sodium based. Less common is potassium-based salt.
I use sodium-based salts. I have read that this might not be beneficial for plants. I have no experienced this, there is no problem with my plants.
However, I have also read using potassium-based salts is better because plants actually use the potassium.
My guess is that as long as there are enough minerals remaining, there will be good plant growth.
As for whether you should use softened water or not, it depends. Most plants themselves are highly adaptable to water conditions. They will adjust whether it is hard or soft, given moderation. Advantage I see in going w/o water softener is saving on the amount of softening salt used. Also depends on moving inhabitants you keep. Some fish/shrimp like soft, some like hard.
I think this works to your advantage because you can use hardwater for some fish, and switch to soft water for others.
In terms of effect on water parameter, softer water will have less buffering capacity. This means if you inject CO2, pH will decrease faster than in hardwater.