Question: Dip in tail

[Silverazlan]

Is my little lotl tail alright? Ive had her for months now and Ive just notice her tail. The bleeding is from her being too active but the little dip in the middle of her torso and tail is concerning. She is active, likes to go around the tank. Ph level sometimes reach 8.0 but I change 20% of the water ever other day, Nitrite level is good, temp is good tank located in an ac room. Her diet is stable and on schedule. She doesnt seem stressed.

The decor is not sharp, ive sandpapered it down.

 

[wolfen]

test the water parameters with a freshwater liquid test.
if you haven't got a air-stone get one.
cool for a human doesn't mean cool for a axolotl, there are numerous things that will warm a tank up, such as the filter pump, get a thermometer to check temp.
test the ph of the tap water and the tank to see how much difference there is. the ph needs to be stabilised as fluctuating/swinging ph is stressful, if you can get a kh gh liquid test do so.
at this point in time the tail doesn't look to bad. this isn't to say not to keep a eye on him/her, just that it isn't a worry at this point in time.