Fish gasping for air after water change

[Tifta]

It;s been awhile since I've been on here.

So I have had my 55 gallon tank up for 4 years. I decided to do a 40% PWC like I normally do. I added my prime and water. I woke up this morning, and noticed that two of my fish had died, and the rest were gasping for air at the top. I immediately did another PWC which was about 60% and they seemed to be acting fine after that. Well a few hours later they started gasping again at the top of the tank. I have no idea whats going on. I did have a party last night, and I am wondering if someone might have contaminated the water or something. I also thought maybe since it's been so hot so I added a airstone and air pump to see how that goes.. The temp is 80 F

With as many PWC I have done, do you think another one would make things worse?? Some ideas and help would be greatly appreciated!

 

[jetajockey]

I think the first step would be to test the water for ammonia and nitrite. What was your PWC schedule prior to this? What about pH?

 

[Mark388]

Those are pretty big water changes and you may have shocked them if the temp was to drastic of a change. Gasping is a sign of low oxygen normally due to high temp so adding a air stone would help.

 

[jcolon]

You might want to check with your town/municipality to see if they did any work or treatment to the water lines. I've read similar threads where experienced members had fish die after a routine PWC... Turns out the town purged the water lines.

It's threads like these why I no longer do large (40%) pwc's at once. I do 5 -10 gallon increments throughout the week till I've done 25 - 30gallons worth.