White Streak On Tail Of Swordtail

[molver]

Hi again,

I've noticed my swordtail has a white streak on the lower portion of its tail. It's a little faint, and I only noticed it today, but it's definitely not normal. And my camera makes it much less noticeable, it's more like a streak that goes right from the edge of the tail to the base. Does anyone have any idea what's wrong with it?
 
It's still active and happy, and pregnant!
 

 

[FishMonkey]

It looks to me like they have been nipped by another fish, but i'm no expert. I'm sure someone will correct me if i'm wrong.
 
How big is your tank?
 
How long has it been cycled?
 
What are your water stats?

 

[molver]

I'm not sure about the water parameters, I haven't had the chance to test it for a couple of weeks.
 
My tank's been cycled for 3 months now, and it's a 20 gallon.
 
I think it's fin rot, the streak is getting more noticeable.

 

[molver]

It's getting worse!

The tail is starting to get frayed. She's still very active and stuff, but this obviously isn't good.
 
I know I should get my water tested, but I just don't have the time right now to go get my water tested. I have to be at school every day, pretty much all day for the next 5 days.
 
I'm treating with Melafix, and Pimafix and it's been two days now.
 
I will buy another product if necessary, but I would really appreciate it if you could recommend a product from one of these links: (http/www.petsmart.ca/fish/disease-treatment/cat-36-catid-300009) or (http/www.bigalspets.ca/fish/health-supplements-medications.html)
 
That's pretty much all I have access to. And I'd like it if it isn't expensive, I'm only a student. 
 
Thanks so much. This is one my first fish, and it would mean a lot to me if I can save her.