Ich and new tank setup

Question
I have had a tank for about 2 weeks now and have followed all the guidlines to breaking in the tank - i let the filter run on its own for almost a week with no fish and tested PH to make sure everything was ok.  Added 6 tetras (not sure what kind but the fish store told me they were hearty - they are red with a black spot on the side) to a 28 gallon tank to cycle the tank.  All was well, ammonia levels were ok and i was doing weekly 25% water changes.  I left for a weekend and when i returned 3 fish had serious ich infections.  I just raised the temperature to 80 degrees and started treating with malicide but was confused at how quick and why this happened?  My main concern is that 3 or 4 weeks down the road when the tank has fully cycled i want to be able to add some more expensive, bigger fish but do not want them exposed to any diseases.  I do not have a hospital/quarantine tank because i live in a tiny (read - TINY) apartment in New York city.  I have kept fish before without the slightest care for water quality, breaking in the tank, and most of the time they were ok.  now that i care, i already lost one to ich - any suggestions?  can i safely add more fish in a few weeks and any idea on why the fish were overly stressed as to break out in ich?

Answer
Hi Steve;

The stress of having a new home will cause ick outbreaks. The parasite can easily take advantage of them at that point. It's also possible they were infected when you bought them. It's hard to blame the fish store though. These diseases are present everywhere in most of our tanks just waiting and can attack any fish that are stressed. Fish store fish can be moved several times before they get to your house but you don't always know that. From fish farm to wholesaler, from wholesaler to your fish store, from fish store to your tank can all happen in just 3 or 4 days. That's a lot of stress! The rest of the same fish left at the store may be completely all right because they didn't experience the extra stress of being moved once again to your house. It's helpful to choose fish that have been at the store for a few days. It gives them a better chance to get over the stress of their last move.

A quarantine tank is good to have but if you don't have room for one, you don't have room. Do the best you can to choose fish from tanks that look healthy and "look first, buy later". Find out what day new fish arrive and buy them a few days after that.

Keep up your weekly water changes and your fish will be healthy long term. You are doing an excellent job so far, just a bit of bad luck is all.

At Your Service;
Chris Robbins