Using water from a water softener?

I've always been under the impression that softened water, e.g.,
Culligan water softened water etc. is not a good choice for fish.
My understanding is it takes the calcium and magnesium ions out
and replaces them with sodium ions. Apparently the thinking is the
fish need the ions that are removed.

I'm donating my second small RAS (recircuating aquacultur system), fish, and feed,
to another local high school and I've just found out the entire school is on a
water softener. I told them that wouldn't be a good choice. They
do have access to well water but it may be problematic to hook up
to that.

Will it work? Or should they only consider the
well water? BTW, the ground water here is really good (I'm within
a stones throw of this high school), but the iron from 2.5 to 5
mg/l is a PITA. However I've come up with a really simple cheap
way to remove it without using chemicals for small scale
applications of about 50 gpd.

The species that will be in the tank are bluegills if that
matters.

Thanks!

Edited by az9, 28 September 2012 - 11:18 PM.

Have them set up an aging tank where they can introduce some of the locally available soluble lime to restore hardness. They may need to measure hardness to determine amount of lime and time required to get hardness to desired level. After method worked out, stop measuring hardness to save time.

If it is worth it to them, a plumber should be able to install a T and faucet on the incoming water supply pre-softener, though this may be along distance from the RAS.

The added sodium from the softener won't bother bluegills at all - they can take a lot of salt. Add the missing Ca & Mg back in with lime, aragonite, or oyster shell like Jim suggests. That will be probably be more feasible for the school than redoing the plumbing.