Hello, so I have had 3 corydoras in my tank for around 5 months now and they have been completely fine so far however 2 days ago I noticed a small white lump on his back fin and decided to monitor it. It has not gone away so am wondering if anyone knows what it is and how I can treat it. I have attached a photo of it. It is not displaying any other in usual behaviour. Thanks for any responses!
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