Is it safe?

[bcutajar]

So ive had 6 corydora sterbai in my tank which appear to have red on their sides as seen in this picture




5 of the smaller ones have predominant red colouring. This is not due to ammonia poisining as the levels in my tank are both 0 for ammonia and nitrite.i also have 20 cardinal tetras in my tank which love life. All the fish in the tank eat when they are fed and are continuously moving.

My question is that i have some discus fish at my local fish shop on hold for the next week is it safe for me to put them in? Or is this red some sort of disease?

 

[Mcor]

Ok, my immediate thinking was ammonia or nitrites, but your water is fine. I've tried a google search too but it all comes back as ammonia, nitrites, or some sort of external irritant. Really at a loss as to what is going on. I would hold off on getting more fish until you figure out what is going on. Something, somewhere, just isn't quite right. Hope someone is able to help you figure it out!

 

[Fidgetromeo]

My Cory's have always had a bit of red there like urs, water tests fine and they seem to be healthy, could just be markings I guess

 

[bcutajar]

Thanks for the response, i went back to the same fish shop an they said theyre just waiting to colour up which i dont understand because all te ones i their tanks have red, maybe theyre just covering their backsides. And yes my water levels are 100% fine