One of my female guppies is sick. She’s become skinny and now is becoming quite pale and even transparent! I looked up a ton of fish diseases and parasites and stress symptoms but I’m still not sure.

As far as I can tell she has no white spots, fuzz, unusual poop, or any other tell-tale signs of specific illnesses besides simply growing frail and pale.

I have quarantined her but I don’t have a hospital tank so she is literally in a bucket which, unsurprisingly, isn’t helping her at all, but I don’t want the other guppies to become infected.

I checked ammonia and nitrite a short while ago and have done recent water changes.

Can anyone tell me what’s up with her? And if it's contagious?

None of my other fish are showing any symptoms luckily but I know they can take a while to show symptoms as well.

Further circumstances:

Echo (the female guppy) came with two other guppies, another female and a male. They were probably a couple months old when I got them. I had them in dorms at school and the guppies all acted completely normal, except that the male seemed to only chase echo and not the other guppy. I also added a cory catfish along the way.

Despite having the guppies for 4 months they didn’t have any fry.

Then I moved home. Once I was home I added new ornaments and a second heater to raise the temp a bit to make the guppies breed. Shortly after, one of my females (not echo) died. I thought “this happens with fish” and wasn’t overly concerned.

I didn't want my male stressing Echo out so I bought another batch of guppies and added them to the tank. Shortly after my male guppy started wasting away. I thought the new guppies may be bullying him so I put him in a breeder box and then eventually moved him to a bucket so it wouldn’t affect my other fish. He also died so I kept a close eye on Echo for a while.

It’s been about a month since the male died and Echo had adjusted well with the rest of the guppies and was healthy and active.

However just the other day I noticed she had lost a ton of weight over just a few days. I removed her from the tank. She is the last of the three from the first batch so I’m really hoping this is just an issue from that first batch and won’t affect my other guppies. Thoughts? Please help!