Sunburst Platy?

[insecurity]

Hey fellas. I got my first sunburst close to a month ago, and I just came back from the LFS with two more.
As the newcomers were acclimating (and still are), I took some time to look at the finer details of the tank. It was at this point when I found my original Platy (female) with deep brown/blackish spots on its head. Sorry I don't have any pictures, because this girl is very skittish and likes to hide. Is there something wrong with the platy?
Some points: 25% PWC w/ gravel clean performed yesterday. Tested water- all ok. Yesterday the Platy didn't have any strange discolourations. I find it deeply disturbing that this discolouration happened overnight. If it helps, I often find my male swordtail hanging around the Platy, but it's not harassing the Platy.

Any tips/help/suggestions would be greatly appreciated.

 

[Ljk09]

Is your tank cycled? What is your ammonia reading? It may be an ammonia burn, it could be some coloring on her you're just now noticing. It would probably help if we knew your readings of ammonia, nitrite, trate, stuff like that. I know you said they are ok, but are you using strips or liquid? Strips can be very inaccurate.

 

[tamtam]

What were the levels from your test? Did you test it before the change or after? Ammonia burns can turn blackish when they begin to heal, sort of like scabbing over. She may have had the burn that you didn't notice and it's now starting to heal.

 

[insecurity]

Liquid.
Pre-PWC- ph:7.2 / Ammo: 0ppm / Nitrite: 0ppm / Nitrate: Less than 5ppm
Post-PWC- ph:7.0 / Ammo: 0ppm / Nitrite: 0ppm / Nitrate: 0ppm

 

[tamtam]

it sounds like your tank isn't cycled yet. If you are going through a fish in cycle and had any spikes in the last while this could have caused the ammonia burn and it could be just healing now. I don't think it would be too far of a stretch for it to take a week or more to get to that healing "scabby" stage. It's really all I can think of. Sorry I'm not more help

 

[insecurity]

it sounds like your tank isn't cycled yet. If you are going through a fish in cycle and had any spikes in the last while this could have caused the ammonia burn and it could be just healing now. I don't think it would be too far of a stretch for it to take a week or more to get to that healing "scabby" stage. It's really all I can think of. Sorry I'm not more help

tank is fully cycled- i'm a bit nuts when it comes to cleaning- PWC every 1-2 days- my fish love new water

 

[Ljk09]

What is a partial water change to you? 10% or 70%?