Illness/Sickness: My Axolotl's gills are degrading

[Pooboodeltin]

Hello, I've had my axolotl for a little over a year, and a few months ago I noticed something wrong with his or her gills. They seem to be degrading. He/she doesn't seem to be stressed out or anything. What do I do?

 

[NexSocius]

What are your ammonia, nitrite and nitrate levels?

 

[Pooboodeltin]

Here are the water parameters from last week when I tested it:
Ammonia-0ppm
Nitrite-0ppm
Nitrate-5ppm

Here are the ones for today.
Ammonia-0ppm
Nitrite-0ppm
Nitrate-160ppm
That is a MASSIVE jump. And I think I know exactly what caused it. I use a filter media called Biohome Ultimate. It kept my 18 gallon cube tank at a constant ammonia-0ppm nitrite-0ppm nitrite-0-5ppm for many months by supporting both nitrifying and denitrifying bacteria. But apparently, if you use a water conditioner that detoxifies ammonia, nitrite, and/or nitrate it will kill off all of the denitrifying bacteria. I must have used the wrong water conditioner for the last water change.