Piranhas

Question
Today I cleaned my tank and added some water to the tank and all the feeder fish we put in yesterday died within two hours of adding fresh water. Then one of the piranhas died and the other ones are swimming near the top of the water. What can I do to keep them from dying? Also, there was a frog that was added when we added the feeder fish. Would that affect the piranhas? Thank you for your time and expertise

Answer
Justin,
Did you clean the tank completely? If all the fish are at the top of the tank, they are telling you that there is little oxygen in the water. You should check your filter and see if it is working properly. You can also add an air stone to the tank to help with that problem. Also, if you have too many fish in a tank that is too small that too can cause this problem. I am assuming the frog was put in for food. Unless you are raising your own live food, you run the risk of contaminating your tank with sick fish. Feeder fish are mass produced and if you use them, it is best to quarantine them for 2 weeks so that if they are sick, you will know it before adding them to the main tank. I think the biggest problem is the lack of oxygen. I do not know who many fish you have or how big the tank is, but 1  piranha should be in a tank no smaller than 40 gallon depending on the age and size. 40 gallons is for 1 adult piranha. Also, make sure you are adding a good water conditioner, and that you are doing weekly water changes.