Fish Dying Suddenly

[CleverBs]

So I have had a school of 15 serpae tetras for the past 2 weeks and my water was perfect Ammon: 0 Nitrite: 0 Nitrate: 5ppm PH: 7.8ish Temp: 80
so my water was stable so i decided to get a school of Cardinal Tetras 10 of them. Over 2 days 6 died one by one but only one ever showed any sign of death. On more then one occasion I would see the school swimming around with all their members and go do something for 15mins look back and one would just be dead on the bottom of the tank. Then last night 2 of my Serpaes died and I got 15 all at once 2 weeks ago and they all did great never lost a single one and they died the same way the cardinals did. What could be going on that im not seeing? All the colors on the fish are great, they are bright and the fish are very active and eat well.

 

[dskidmore]

How big is this tank? 5 ppm Nitrate, unless you do a lot of water changes, that tank may not be fully cycled. You nearly doubled the population of the tank in one day, that's a huge ammonia boost.

I never trust "perfect" water quality numbers, they say nothing about the ammonia processing capability of your tank. I prefer to track ammonia and nitrite over time, and see them spike and come back down. Given your current death rate, you will likely see ammonia spike even if there was no previous problem, so that is your first problem.

Do a bunch of large water changes, then let everything stabilize for a few weeks. Test ammonia/nitrite every few days to make sure it's stable. Next time add fewer fish at a time, just 2-3 per week. If you have to add a lot of fish at once because you're mail ordering or taking over someone else's fish, prepare the tank ahead of time by overfeeding before the new fish come, and underfeeding when the new fish come, to try to slowly ramp up the ammonia load instead of all at once.

 

[bruinsbro1997]

The problem is that cardinal tetras, like some other tetras, are usually wild-caught. Wild caught are a lot more sensitive than say tank-raised or tank-bred. You also mentioned that you got these from Petsmart, which might be a problem seeing that the condiitons aren't always the greatest. Have you tried drip acclimation instead of floating the bag? That could help.

 

[CleverBs]

How big is this tank? 5 ppm Nitrate, unless you do a lot of water changes, that tank may not be fully cycled. You nearly doubled the population of the tank in one day, that's a huge ammonia boost.

I never trust "perfect" water quality numbers, they say nothing about the ammonia processing capability of your tank. I prefer to track ammonia and nitrite over time, and see them spike and come back down. Given your current death rate, you will likely see ammonia spike even if there was no previous problem, so that is your first problem.

Do a bunch of large water changes, then let everything stabilize for a few weeks. Test ammonia/nitrite every few days to make sure it's stable. Next time add fewer fish at a time, just 2-3 per week. If you have to add a lot of fish at once because you're mail ordering or taking over someone else's fish, prepare the tank ahead of time by overfeeding before the new fish come, and underfeeding when the new fish come, to try to slowly ramp up the ammonia load instead of all at once.

My adding more then 3 fish is not the issue I do a water test every day with an API test kit, my kit stopped reading Ammonia 5 days ago and after adding my fish every number was exactly the same. so this is not the problem. I have a 75 gallon tank.

The problem is that cardinal tetras, like some other tetras, are usually wild-caught. Wild caught are a lot more sensitive than say tank-raised or tank-bred. You also mentioned that you got these from Petsmart, which might be a problem seeing that the condiitons aren't always the greatest. Have you tried drip acclimation instead of floating the bag? That could help.

I will keep this in mind but it doesnt explain why 2 of my Serpaes died weeks later at the same time as my cardinals are dying.

 

[dskidmore]

Did you get a nitrite spike after the ammonia spike? I would not expect a tank that just finished the cycle to be stable enough to vastly increase capacity.