Corydoras with red belly

[RickHunter]

We found one of our Corys with a really red belly this morning. He seems to have been hiding awhile which is why we didnt catch it earlier. He came out after a 35% water change in the tank. Thinking its possibly the red spot disease (his fins a ripped too). We've moved him to a small  3.5 gallon tank we keep a few snails in to start treating with API Erythromycin. Looking for second opinions. No similar signs in any of the other 9 Corys in the tank he was in.
 

• pH - 7.0-7.4 range
• Nitrates - 20-30 (probably lower as this was pre water change)
• Hardness - (dont have a specific number but we do have water thats on the harder side)
• Nitrite - 0
• Ammonia - 0
• KH/Buffer - (Unknown)
• Water Temperature - 77 F
  
  

Edited October 9, 2020 by RickHunter

[BNye]

My guess would be a bacterial infection, I would just keep treating with the API Erythromycin and see what happens. You could also try using salt if it is not in a planted tank. Here is an article on using salt. https://www.aquariumcoop.com/blogs/aquarium/aquarium-salt-for-sick-fish?_pos=1&_sid=329790e30&_ss=r. I am not sure I would use the salt in the 3.5 gallon with the snails as I am not sure how it will affects snails maybe someone will know better than me or it will be specified in the article.