Please help - black mark above guppy eye??? Disease?

[GuppyFamily]

Hi there everyone, looking for some help as a new guppy tank keeper. Running a 10 gallon tank with good filtration very clean Clearwater, been up for about two months and one guppy started behaving odd and has developed a black mark above its left eye.  Currently have him in a quarantine tank and I’m treating with erythromycin, but no significant improvement and his eating is way down to almost nothing. All the other fish are happy and healthy. Parameters are all normal. Have added a small amount of aquarium salt to the main tank about 30 g per 10 gallons, just for general health.

 

Edited May 6, 2021 by GuppyFamily
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[KBOzzie59]

Any possibility of a picture?

[GuppyFamily]

Took a minute to figure out how to upload, here it is

 

[Colu]

It could have swim into something in the tank black marks usely a sign that it's starting to heal I would monitor for now

[GuppyFamily]

Thank you.  It is possible that the larger male was beating him up?  Could that be the problem?  Didn’t see aggression, but he’s not really thriving and the other one is.  They were the same size going in...

[Colu]

2 hours ago, GuppyFamily said:

Thank you.  It is possible that the larger male was beating him up?  Could that be the problem?  Didn’t see aggression, but he’s not really thriving and the other one is.  They were the same size going in...

It's possible you could separate them and see if that helps if you have breed basket or another tank to put him in

Edited May 6, 2021 by Colu