New to the site, new to aquariums. Bought a 20 gallons for my daughter, I set set it up Christmas day. Waited two weeks before adding three black skirted tetras to help with cycling. One week later all is well so I add three sunburst platys. One week later, two platys are dead and all three tetras are reeling from ich. I've been medicating tank, changing water appropriately etc. My question is should one use a quarantine tank? I'm convinced I was sold sick platys (I wasn't smart enough to spot a sick fish, a little smarter now) who infected the tank. I keep reading about using a quarantine tank for new fish but that seems like a large expense -- i'd basically need to duplicate everything I own and recycle the water after each fish purchase. To use a quarantine tank until I hit my max population of 15-20 small fish seems excessive. I'd be interested in any thoughts about introducing new fish while minimizing the threat of introducing disease to the tank at the same time.