Ulcer? Help please!

[Stevieleigh]

Noticed this ulcer type wound on my boys lower lip. He is eating well still and active. His tank buddy (another axolotl) is fine.
Is it an ulcer or is this Aeromonas hydrophila?
I do a 30% water change once a week. Recently had a colony of possibly water flea building up (see image) so done a bigger percentage of water change to try and bring the numbers down.
Currently my water tests are:
pH: 7
NO2: 0
NO3: 0
Ammonia: 0.2
KH: below 1 dH ** I'm worried about this! I don't know how to fix this?
recently my boy has started displaying courtship and dropping sperm banks. The other axolotl is a female. I'm not interested in breeding them and as far as I know nothing has come of it. Do I need to get some holtfreters solution or mercurochrome? Salt water bath? Or find a vet?
Thanks
Stevie-Leigh

 

[GalLuvsAxolotls]

If it has gotten any worse, I would find a vet to take a look at your axolotl. Treatment without knowing exactly what you are dealing can be extremely hard on your axolotl and may not clear up the problem. Even salt baths can be quite hard on them!