Is my platy ill?

[Dragonbot]

I think my common platy is ill, but I have no idea what it is or how to treat it. This is the best photo I could get.


She doesn't have this anywhere else, just that specific spot. She seems okay; active, responsive and eating fine. I haven't introduced anything new to the tank. I recently did a large water change to deal with a nitrate issue, but it never got to dangerous levels. The pH is a bit too acidic, which is something I'm probably going to tweak now unless one of you scream not to. Nitrite levels are 0, Nitrate levels are 20 ppm? The only thing new to the tank would be API Stress Coat+, but I don't see how that could have caused this. The tank is fully cycled too.
What is this? Do I need to run out and grab medicine?

 

[SM1199]

I'm going to be the one to scream "don't mess with your pH." It can do more harm than good as it is safer to have a sub-optimal, but steady pH, than it is to have an optimal but unsteady pH. Especially in these domesticated fish that are much less picky about specific conditions as compared to their wild ancestors.

Platies sometimes have a spot of thin or missing scales and/or pigment on top of their head/back, right in the center. Which is what it looks like here. Keep an eye on it to see if it becomes larger or raised, in which case I'd be a little more concerned - but right now, definitely no meds, especially since she is acting completely normal.

 

[Dragonbot]

I'm going to be the one to scream "don't mess with your pH." It can do more harm than good as it is safer to have a sub-optimal, but steady pH, than it is to have an optimal but unsteady pH. Especially in these domesticated fish that are much less picky about specific conditions as compared to their wild ancestors.

Platies sometimes have a spot of thin or missing scales and/or pigment on top of their head/back, right in the center. Which is what it looks like here. Keep an eye on it to see if it becomes larger or raised, in which case I'd be a little more concerned - but right now, definitely no meds, especially since she is acting completely normal.

Okay, thanks!