accumulating salts?
 

I'm kind of new to gardening, I'm growing cacti and succulents in clay
pots. If I use rainwater there won't be accumulation of salts right?
The fertilizer I'm planning on using (DynaGro) has calcium in it, this
isn't the same as the calcium carbonate that accumlates in pots right?
Also I have one cactus that is in a pot that I've had for three years
and watered with tapwater. Should I repot it? it got some damage to
the stem, i think just from overwatering, but seems to be growing ok
now. thanks for any help.
andreyev