penn plax cascade 1000 & my fish

[muggiesloose]

just installed a penn plax cascade 1000 (upgrading from an Aqua Tech power filter), to a well established stock. Many of the fish have been in my aquarium about 2 years. Now it seems like the fish aren't getting enough oxygen. The fish that normally swim in the middle of the tank also closer to the bottom half are now swimming very high up a few even swim at the surface. some of the fish seem to be breathing very fast. Also my cory's keep swimming to the top, it looks like thy are taking a breath.
If anyone has ideas as to what could be causing this please let me know. Your help will be greatly appreciated.
Thanks everyone.

 

[Toad]

Did you swap the old filter material into the new filter?

Sent from my SM-G930T using Aquarium Advice mobile app

 

[muggiesloose]

I did not

 

[Toad]

I'm sorry to say this but you've crashed your tank :/ Most of the bacteria that takes cares of the waste your fish produce (other than what you take care of with water changes) is in the filter media. Without swapping that over the waste will build up very fast and kill your fish. You'll want to read up on fish-in cycling and keep up with water changes, as you're basically starting over from scratch.

Sent from my SM-G930T using Aquarium Advice mobile app