Water change, new fish, fish are dying.

Question
Hi,

I have a 30 gallon tank and yesterday I changed almost 100% of the water in my tank, it had been so long since I had changed the water I thought it best to clean it all. I also, yesterday bought 3 new fish a small catfish and 2 small angelfish and added them to my tank with 2 golden barbs. 5 minutes after adding the new fish one of my barbs died. I had thought that it was the catfish that killed the barb and so I removed the catfish from the tank and put it in a separate bowl (I was planning on returning it to the store tomorrow) 10 minutes after separating it, it died as well. Five minutes later my second barb died in the tank, leaving just the 2 new angelfish. The angelfish don't look good and are staying right at the top of the tank. I know that complete water changes aren't a good idea, and fell totally responsible for the death of these fish (i actually cried over it). I checked ammonia, nitrates, nitrites and pH and surprisingly all are fine. I don't know exactly why the fish died, and if there is anything I can do to save the remaining angelfish. I would be so thankful if someone could help me.

Thanks

Thanks,

Answer
Hi Cheri,

The reason why they died is most likely due to the water change. NEVER change more than 30% of the water at a time. If you change 100% of the water, then you will lose all the beneficial bacteria which remove toxins, such as ammonia, from the water. This is the most likely cause of death. Ammonia and other toxins are produced from decomposing fish waste. Since all the bacteria are gone, the ammonia levels build up, killing your fish.

A second reason why the water change killed your fish is because the temperature of the new water was not properly adjusted to fit your fishes' needs. For example, if you used cold water, then all the fish would have died in a few hours, since they are all warm-water fish. another reason may be due to the fact your water's pH value was different than the one your fish are used to.

The catfish didn't kill the barb, especially if it was small. catfish prefer to be on the bottom of the tank. It died most likely because of temperature change. Never keep fish in a bowl, because bowls do not provide filtration to develop beneficial bacteria to remove toxic compounds. a bowl is like a toxic cesspool for fish, and not even goldfish (a common misperception) can be kept in a bowl.


I won't say anything more about how your fish died, because you probably know not do do a 100% water change any more.

Here's how you can save the remaining Angelfish:
-Make sure you have a HEATER, set to approx 78F, if not set to approx 78, raise the temperature slowly by a couple degrees per hour.
-Change 10% of the water every day, for two weeks(sounds bizarre, but you need to do this in order to reduce the toxic ammonia buildup that results from the loss of beneficial bacteria.
-Optional: Get a pH test kit and adjust the pH with a pH chemical if necessary
-Optional: Add live plants to increase oxygen levels.

Good Luck, and I hope your fish recover!