If you are cycling your tank with those damsels, I would see if you can take them back to your LFS
and get two cocktail shrimp from your grocery to finish the cycle. For one, it is inhumane and they might not make it. Two, once damsels get older, they can be very aggressive, and with your set up, you might have a hard time catching them or adding other fish to your tank.
will replenish anything your critters use. Unless you have a bioload that requires more than you have in the water. I have read that most just increase PWc
if they find their tanks being depleated of minerals and such. Personally, I try to keep it as natural as possible.
I don't use a skimmer, so som one else will be along to help you.