Platy

Hello
I have a 54 litre tank, unheated, which has two platys and two fancy goldfish.
The two platys - which I was assured were both males - were my 'practice' fish after I had cycled the tank and they swim together closely (shoaling behaviour).
Over the last month or so, the smaller of the two fish, whilst swimming and eating normally, seems to have become smaller, less colourful and always has its fins scrunched up.
Is he ill? I don't think he's injured. Is there anything I can do for him. Or is he doomed?
(They live in the tank happily with the two goldfish and there does not seem to be any problem between the two types.)
Thank you for any advice you can give me.

Hi and welcome to the forum

They are both male hi fin platies. Chances are the bigger male is bullying the smaller one and it is not getting as much food and feels stressed out.

Livebearers live in groups consisting of lots of females and a few males. If you add lots of plants and a few more platies, then the stress should reduce and any bullying will be spread out over all the other platies instead of just one. The best plant for them is Water Sprite (Ceratopteris thalictroides). It floats but also does well when planted in the gravel

Thank you for your reply. And confirming they are both males.
You'll be pleased to know that he is still doing fine
Sadly, in this heat wave, I have lost one of my large goldfish, despite having two pumps and an air stone in the tank.
So I may decide to get more platys shortly.