unless they are falling apart just clean them once a week or twice or however much you change the water.
I disagree with sludge monkey you do not need to change your filter pads at all, if you get carbon type ones to help with water quality, again im not going to go into water quality as my boyfriend is an aquatic specialist who works with all sorts of animals!
If you have issues with ammonia or whatever changing them can help, but water changes and bacteria can do this as well like nite out bacteria, CHANGING the filter pads when you dont need to is ridiculous because your chucking away loads of bacteria that aids in the breakdown of ammonia and nitrite.
As well as it being costly its a waste of time getting new ones unless your going through hell with water quality, just wash once a week or every 2 weeks or when you do your changes in your water .
It seems quite offensive you suggest to keep an axolotl you must also keep water as that was what the question was, were all aloud to ask questions!
And a sick axolotl will be regularly replacing the filter pads or sponges because your chucking away the bacteria that break down ammonia and nitrite. So for a healthy axolotl = not changing filter pads that much, they act as housing for bacteria, just clean them regulary in tank water and youll be fine, dont get flobbed off with any rubbish that you need to spend lots of money to help reduce your filters efficiency, if you want to buy anything for your filter to keep water quality up buy some bacteria like nite out works wonders in reducing nitrite and ammonia, and safe with axies!!
Hope this helped and if you dont want to read the above basically dont change your filter pads just wash them unless they are falling to bits

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