Intro (returning member) & water softeners...

["Gitte" <eladeria at rogers_com>]

Hi there,
 
I'm just returning to the list after a long absence.  I've been keeping
planted aquaria for about two years.  I am having really good success
with my 50-gal. planted tank, but a lot *less* success with my 20-gal.
and 10-gal. planted tanks.  More about them another time.
 
Soon I will be moving to a house that has a water softener.  I don't
think that any conveniently-located taps in the house (if any at all)
bypass the softener.  I have read some messages in the archives on this
subject.  I would like to make sure I'm not oversimplifying.  What I
have understood, is that the sodium added through ion exchange would not
be a huge problem, but that I would need to add calcium and (was it?)
magnesium to the tanks in order to have continued success with planted
tanks.  Is it that simple?  I am not much of a chemist (understatement),
so by necessity I'll ask for a not-too-technical answer.
 
My other alternative in the summer months only, will be to use lake
water from Lake Simcoe (Ontario), but that is currently available
outside the house only - there is no lake water tap inside the house.
Therefore it would be unheated (unless I gather it in barrels and heat
it with an aquarium heater).  Would the lake water be a better
alternative during the months it is available?
 
Thanks!
Gitte