Axolotl foot problem, please help

[Slime]

Hello,
This morning I noticed my axolotl Zero's front feet were looking strange, it looks like they became stubbier and there even appears to be exposed bone on a few of the toes. I checked the back feet and they look better, but one looks like it's starting to have this problem. I don't know when this first started but looking through my photos this is very recent and has only started within the past month.
My water test strips show the parameters at:
Nitrate: Possibly above 0 ppm, but below 20
Nitrite: 0
pH: Between 7.5 and 8.0
KH: 180
GH: 180
I have not been able to check ammonia yet. I haven't noticed any signs of stress and she is still eating. My tank has live plants and a sand bottom. I did recently switch out the canister filter for a new one, because my old one started acting up, it was making a noise and had a weak flow. I also removed a hang on back filter I used to have on the tank so I could add a metal screen lid to keep my cat from getting in. The current Canister filter I'm using is the Marineland Magniflow 180. I don't have experience with tubbing or treating an axolotl illness and I don't know of an exotic vet in my area. Please help, I can tell something's going on and I don't want it to get worse.

 

[Slime]

A couple other photos (the last one of these is the healthy foot), I couldn't upload these at first due to the file size

 

[wolfen]

your sand looks to be a bit coarse which can cause damage to his/her digits when he/she digs around hunting for food.
be aware that any changes to substrate or filtration can cause fluctuating levels and should be monitored until everything has settled.
try to get a liquid test kit for accurate readings and ensure that ammonia is tested.

 

[Slime]

I picked up a liquid test kit today, I was able to test the ammonia and the levels are at 0. I also added two Indian almond leaves as I was reading they can help with certain things like bacteria that can cause this. I forgot to mention that my tank is 29 gallons.

your sand looks to be a bit coarse which can cause damage to his/her digits when he/she digs around hunting for food.
be aware that any changes to substrate or filtration can cause fluctuating levels and should be monitored until everything has settled.
try to get a liquid test kit for accurate readings and ensure that ammonia is tested.

I believe the sand is pool filter sand, but I've never changed it. I've had her in this tank for a few years now, I'm unsure why it would only start damaging her toes now. I'm a bit worried that changing out the filter could be what caused this since that would line up with when this happened. I don't know if it could be that though since the tank parameters are normal as far as I can tell.