Odd Bala shark behavior

[AZLenore]

I recently set up a 150 gallon freshwater aquarium. The first fish I got were 3 Bala Sharks each about 3 to 4 inches long. This was about 4 weeks ago. They did great but when they fed they would go up to the surface of the water and suck in the food, along with quite a bit of air. You could see the air bubbles go out their gills. I have had Balas before and don't remember them doing this.
About two weeks ago I added about 25 Tetras and everyone is getting along very well. The water quality is stable, no signs of disease or injuries, everything is great. Except...
Three nights ago, right after I fed them, I saw one of the Balas upside down on the bottom of the tank. His respiration seemed labored and I was ready to pronounce him a goner.
I got up the next morning expecting the worse and was very surprised to find all the Balas in apparent good health. Three days later and everyone is alive and kicking.
As the fish was in obvious distress I would like to take steps to avoid the situation in the future, but first I have to figure out what caused it.
Could the sucking in of air be in some way related?
I appreciate any thoughts you might want to throw my way!

 

[redsea]

Welcome to the forum!

 

[melosu58]

Moved to FW general Discussion. More answers there as this is the welcome wagon.

 

[librarygirl]

Did you cycle the tank before putting fish in? If not, the fish are probably suffering from ammonia poisoning.

Do you have a test kit to test the water (ammonia, nitrite, nitrate)? If not I'd get one ASAP (liquid tests are more accurate than strips).

First thing I'd do is a massive water change, 50% (I hope you have something like a Python or you'll be lugging a lot of buckets lol) using a good dechlorinator (Seachem Prime is best if you can get it). Then get a test kit. There's a link in my signature called "new tank wish fish;" it'll guide you through the process.

Let us know how/if you cycled the tank and post your water parameters (ammonia, etc) as soon as you get a test kit if you don't already have one.