How to safely treat white spot on Danio's back

Hi there,
All of my fish are seemingly healthy, active, and eating well. All of them except, one of my Zebra Danios. He has been hanging out more than usual in the back of my tank for the last several days. It's obvious he's not at his best. He still comes out; does a little bit of chasing (though not like he has done for the 7 or so weeks I've had him). He also still swims with the gang during feeding time (though he doesn't eat much if anything). I did a partial water change on Sunday and another WC yesterday. Ammonia and Nitrite are 0 and from what i can decipher Nitrate is around 15-20ppm -- API Master kit for Nitrate is hard to read, so I'm ordering the Salifert liquid test kit this evening. I inspect my fish daily, and today noticed a white spot on my Zebra Danios back. Please See picture. A woman at one of my LFS said it could be fungal, but she didn't see the picture. Btw, I did add a couple Anubius plants a week ago. I did give them a controlled and diluted bleach dip, but perhaps some microbe tagged along into the tank with them.

I'm not sure how to proceed as it's my 1st time encountering a possible disease. Thanks in advance for any advice.... . If we decide I should medicate, what the pros and cons? Would it be best to start with the least amount of chemicals - like aquarium salt? Would i want to move the little guy into my quarantine tank? FYI, I do have a new bottle of Kordon Rid-Ich Plus that "controls ich and other protozoan or fungal extermnal diseases". Thank you so much for your time and help!

It is hard to tell what it is from that photo I'm sorry. The photo almost shows the rainbow with a mark on it as well.

Your picture is not clear.
I guess it's either bacteria or fungal infection.

Here's A little better picture. Difficult to get much better. The spot is pronounced and white.

Well I'm leaning toward it being a fungal infection and am going to quarantine him and first treat with salt per ACoop suggestion. Aquarium Co-op says fungal infections can come from poor water quality and also from malnutrition. This little guy is my smallest fish and has tended to eat only very small amounts during feedings. Maybe he's malnourished. Or maybe it's the water... But, from now on I'm going to continue doing weekly WC. Didn't know how important this was until coming here. Thanks!

I would just let him be I think it may be a war wound and should heal on its own, just monitor for now.

itiwhetu said:

I would just let him be I think it may be a war wound and should heal on its own, just monitor for now.

Click to expand...

that sounds sensible advice. He may have bumped into a sharp edge of a rock. I’ll monitor a little while longer. Hospital tank is ready to go, should we need it. Thanks.

itiwhetu said:

The photo almost shows the rainbow with a mark on it as well.

Click to expand...

Nope, just a lot of specific white markings/dots here and there.