Platy With Tail Growth

[ZephyrStarPlaties]

Tank size: 11 gallons
pH: 6.5 - 7
ammonia: 0
nitrite: unsure (will update by next saturday.)
nitrate: unsure (will update by next saturday.)
kH: unsure.
gH: unsure.
tank temp: 23 degrees celsius.

Fish Symptoms (include full description including lesion, color, location, fish behavior): Bumpy lesion near base of tail. Fish acting uncharacteristically aggressive and skittish. The lesion in the same color as the scales, as if it's under the skin.

Volume and Frequency of water changes: 20 percent weekly, will be raising to 30 percent twice a week.

Chemical Additives or Media in your tank: I have an under gravel filter, if that's what you mean by media I added biozyme twice and stopped using it.

Tank inhabitants: Five platies, one dwarf gourami, and three albino cories.

Recent additions to your tank (living or decoration): One more platy and an Amazon Sword. The lesion was there before I got them.

Exposure to chemicals: None

Digital photo (include if possible): Too skittish, even for video

 

[FishBlast]

Is the platy black with black in its fins by any chance?
Also, is the tank cycled?

 

[ZephyrStarPlaties]

Is the platy black with black in its fins by any chance?
Also, is the tank cycled?

The tank is cycled, yes. The platy has a black tail fin, but all the other fins are white.

 

[FishBlast]

Is the platy black with black in its fins by any chance?
Also, is the tank cycled?

The tank is cycled, yes. The platy has a black tail fin, but all the other fins are white.

Well, it sounds like a tumor but I'm not sure. Could just be a wound where it's been nipped or a loose scale. Just change water a bit more frequent. If it doesn't change within a week, I think melafix might work but not sure.