My Glofish Has A Black Spot What Is It?

[Hotsauce808]

My tetra has a black spot on his back/ fun I have no idea what it is

 

[fluttermoth]

Welcome to the forum, Hotsauce
 
I'm afraid there's no way of telling, just from that information!
 
How big is your tank, how long has it been set up, is it cycled and have you tested the water at all? How many fish, of what species, do you have?
 
Is the spot raised or flat? Does the spot have fuzzy edges, or is it clearly defined?
 
Is there any chance you could post a picture?

 

[the_lock_man]

You would also need to tell us what model of Glofish(R) you have - they manufacture at least 3 different types of fish.
 
BTW, having seen your other thread, which says you have a 20l tank, none of the types of fish that Glofish(R) manufacture are suitable for a 20l tank.