What is this?

[Tfred82]

I got home from work and saw a large white spot just below the dorsal of one of my corys. I’m still relative new hadn’t had to deal with any diseases in my tank. He is acting normal, eating swimming like he normally does and I don’t see it on any other fish. I have no quarantine tank so he has to stay in with the rest of them I’m hoping it isn’t ich. 
 

40 gallon heavy planted tank with about 40 animals including shrimp and snails (I know it’s a little over stocked)

I do a 10 to 20 percent water change about once a week

temp is 78

ammonia and NO2 are 0

NO3 is 80 but trending down

ph is 6.4

idk how hard my water is but I know my city water is rock solid

and I use prime when I do water changes. 
 

TIA for any help

[Colu]

With nitrates of 80ppm that can effect fish's immune system cause problems with swim bladder what I would do is a 50% water change to get it down to 40ppm do larger weekly water changes and quick growing plants such as hornwort Elodea floating plants water lettuce Amazonian frogbit red root floaters to help remove excess nitrates you I have seen these with spots on Cory's before they usually resolve with  a small amount of aquarium salt 1 table spoon for 5 and gallons at that level it shouldn't harm your plants and add some Indian almond leaves as they have antibacterial and antifungal properties @Tfred82

[nabokovfan87]

On 10/12/2023 at 6:01 AM, Tfred82 said:

40 gallon heavy planted tank with about 40 animals including shrimp and snails (I know it’s a little over stocked)

I do a 10 to 20 percent water change about once a week

temp is 78

ammonia and NO2 are 0

NO3 is 80 but trending down

ph is 6.4

idk how hard my water is but I know my city water is rock solid

and I use prime when I do water changes. 

Stocking?  (most corydoras don't like temps that high)

PH seems low (indicating Water changes might not be happening as often as need be)

Nitrate at 80 (indicating water changes might not be happening as often as need be)

I am very uncertain what on earth that white spot is and It's very, very difficult to see any detail due to the angle/focus on the photos.  If you can, please try to keep taking some in focus / sharp focus.

That being said, my biggest question would be about what filtration you're running, how often you're changing water, and how much.  You mention 10-20% WC.  I would recommend a 30% minimum right now just for the sake of the parameters you're seeing.
 

Sidenote.... I don't think this is a "heavily planted tank" compared to others I've seen, but for the sake of understanding the setup, please share a full tank shot so we can see the tank itself and setup.

I think if anything, the corydoras may have hit itself on some hardscape and caused a bit of a wound.  The question is whether it's showing any indication of bacterial or fungal issues right now.

Edited October 15, 2023 by nabokovfan87
added vid