Death In a New Plant Tank

> Last Night while doing my weekly 25% water change all 3 of my black mollies
> died within 12 hours.

> Should i buy one of those fancy kits for transfering water from the tap?
> Should i put my water in a barrel for a day to let the Chlroine evaporate?

This last comment implies that you are not treating your water before
adding it to your tank.  Do you like living dangerously?

Although many folks don't bother treating tap water when doing water
changes, it is a fact that all municipal water has chlorine in it (EPA
requires this). The exact concentration depends on lots of factors and
can be highly variable over the course of the year.  During the
summer, for example, chlorine concentrations are generally higher to
cope with the warmer water temps. If you add enough chlorine to your
tank during a water change, you will kill your fish.  Even if you
don't kill them, you are probably stressing them.

Local fish stores in Durham have recently complained about "bad
water". I have no sympathy for them.  Sodium thiosulfate is so cheap
that there is absolutely no reason not to use it. Just because you've
"never had a problem before" doesn't mean you won't next week.