I’m going to be blunt here because I think the responsibility is being placed in the wrong spot.
Ich exists on wild fish — that’s just reality. Most fish carry it at some level, and it only becomes a tank-wide problem when stress allows it to explode in a closed system. When every fish in a display suddenly shows ich, that’s almost always a system or handling issue, not something that came in on one single fish.
Freshwater dipping all of your fish after losing one, assuming that fish “brought in disease,” likely added a massive amount of additional stress. A dip doesn’t cure a tank, and doing that across multiple fish can push an already stressed system over the edge.
If the store were selling visibly sick fish, we’d expect to see widespread losses from multiple customers and from their own systems. That pattern usually shows up fast. One tank crashing after a stressful event is a different scenario.
The introduction of a new fish, aggression, hierarchy shifts, instability, and then multiple freshwater dips — that combination is far more likely to trigger a full ich outbreak than a single fish “infecting” an otherwise stable system.
This isn’t about defending a store. It’s about being honest about how ich actually behaves in aquariums. Once it’s in a system, stress is what determines whether it stays manageable or becomes a tank-wide problem.