Fish Died Upon Transfer To New Tank?

[parallax]

I have two fresh water aquariums, one 10 gallon, the other 30 gallon. I had a large gold fish in the 30 gallon, and sadly it died a few weeks ago. In the other tank, I had a few tropical fish: an algae eater, a couple tetras, a few catfish, and two zebra fish.

I decided to transfer the tropical fish into the larger 30-gallon tank. I left the orginal water in the 30 gallon tank (which had been sitting for a few weeks), I added a heater, added some water conditioner/dechlorinator, and let it sit a few days until the temperature was the same as the 10 gallon tank. I transferred the plants from the 10-gallon to the 30 gallon, and then transferred my fish.

All of them died very fast, within 10-20 minutes, except for two catfish, which I transferred back to the 10-gallon in hopes to save them. So far they are OK. What did I do wrong? Since the 30-gallon originally had a fish in it, shouldn't the water have been OK (colonized with bacteria)? Could the pH have been different? I didn't check that.

Should I completely empty the 30-gallon and restart from scratch before buying new fish?

 

[my fat fish]

sounds to me like you have no choice but to start afresh in that tank

 

[dthoffsett]

Since you left the water in the 30gal for a few weeks with no ammonia source (fish) the bacteria colony died from lack of food. Also, you didn't mention what killed the goldfish, I believe certain strains of bacteria can live for quite awhile, so that's a posibilty. If it were me, I would drain the 30gal and sterilize everything, then start over. Once, you have it set up again, you could move the filter, gravel, and any decorations from the 10 gal to the 30gal, in effect cloning it. That would provide enough bacteria for the fish you have in the 10 gal now, and over the next couple of weeks you could add new fish. If you are wanting to keep the 10gal running, I would just do a fishless cycle on the 30gal.

 

[parallax]

Thanks for the post, dthoffsett.

I don't understand how the transferred tropical fish could die so quickly though if it were just that the bacteria from the 30-gallon had died. Wouldn't it at least take hours for ammonia to build up and kill them? Were you also suggesting that the goldfish might have died from an infection, and those bacteria persisted to kill the tropical fish? If so, again, why so quickly?

I don't know how the goldfish died. It was originally a feeder goldfish for an aquatic turtle. But it survived, so we kept it. It lived for over 5 years, then just died. No symptoms. Just one day started flipping out, and died within hours.

 

[dthoffsett]

I don't really know why they died so quickly, just a guess really. I had a similar experience though the fish never left the tank. They just suddenly started dieing, w/very few symptoms. I lost a total of 10 fish in less than 24hours. With Wilder's help, I'm pretty positive I identified the problem. There is a very common bacteria that causes infections (can't remember the name), there are 3 strains found in tanks, the most virulent kills quickly w/symptoms unusual to bacterial infections. So, other than lack of good bacteria, which admittedly shouldn't have killed them quickly, some kind of infection that managed to stay in the tank was my only other guess. Either way, sterilizing and cycling the tank again, should take care of the problem. Just another mistery that fishkeeping is full of. Sorry for your loss, but good luck starting again.