tilapia skin sores

[Demitri Lifgren]

Hi
I'm hoping someone on this forum could help me identify the cause of these sores on my blue tilapia.

Water conditions have been fine.
Ammonia and nitrite levels  close to 0
pH 7.5
Water temp 20-22 degrees Celsius
I have only 10 fish. All about 1.5-3 grams in size in a 30 gallon aquarium

I initially thought it was due to abrasion but now that I've noticed a few fish with the same sores and one has died, I'm thinking it could be a bacterial/fungal infection. Any input on the cause and course of action would be greatly appreciated. Thanks

[Demitri Lifgren]

Thanks for the input. I put one of the fish with sores in a bucket and added salt to a concentration of 2ppt. I'll see if that helps at all