Hi Rex.

There could be a few reasons for fish dying in your tank. Your tank is maxed out on fish capacity, and that is before you added the new fish. Your water parameters are fine (including temperature), so it could be that your fish were competing for oxygen, and a few of your fish didn't get enough to survive.

Another possibility is your new fish could have brought something into the tank, which is why I always recommend a quarantine tank (for at least 14 days). The fish stores have different ways of arranging their tanks. Some have all tanks on the same circulating water, and others only a few tanks share the same water. This means you should check all the tanks in the store, and look for fish showing signs of illness or stress. If there are any stressed or ill fish you shouldn't purchase a fish from that store at that time. Of course, this knowledge will be for your next fish purchase.

The fish you had that died a week ago (the one that behaved oddly), could have been pregnant. The symptoms you described sound like a pregnant fish. Did it have a swollen belly? Sometimes the dulling color is stress, which could be from first time pregnancy.

Since there are a few different possiblities, and I can't say specifically which is the exact cause of death since I can only go by what you describe, and I can't see how the fish was acting or how much it was eating or I can't see the tank itself (as well as other factors), I would suggest that you add an airstone to resolve the oxygen possibility, and try adding stress coat or stress zyme. Keep an eye on the fish that are still living. Keep us posted on any changes in behavior. The sooner you realize a change, the faster we can resolve the issue.
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Phishie
Site Coordinator

"An ounce of prevention is worth a pound of cure."

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