Black Spot on Dwarf Gourami?

[Bettalover333]

Within the past few weeks, my dwarf gourami has developed a small black spot (a few millimeters in diameter) on his side. At first I though it was just an injury healing, as I had heard of injuries turning black while healing. Another thing that came to mind was ammonia burns, but I tested my ammonia levels and they were at 0, so I ruled that out. The reason I wasn't worried about it until now was because it hadn't grown in size at all. However, within the past few days, it appears to have grown and it looks like another spot is also appearing on the bottom fin (Anal fin, i think its called?). None of the other fish in the tank show any signs of the black spots (colored skirt tetras, silver hatchetfish, peppered corys). Any ideas to what this may be? Ive read similar threads, but no one seems to have come to a definite answer. Any ideas to what it may be? I just want my Gourami to be ok. Also, I have a mystery snail in the tank, so don't recommend any medicines that might hurt him please Thanks for your time.

 

[Bettalover333]

Update:

Luckily it hasn't appeared to have grown overnight..... Water parameters are all normal as of this morning. I just did a 30% water change (with gravel vacuum) 3 days ago (I usually do one every 1-2 weeks) Unfortunately I don't have the liquid test kit, so this is all from the paper strips... Should I get the liquid test kit to be sure? Ive heard they are much more accurate. Thanks for all the views, but I'm still waiting on someone to respond...

 

[Supergummy]

Is it a boy or girl?

 

[Bettalover333]

Gender

He is most definitely a male. His dorsal fin is pointed and his colors are much brighter then any females I've seen

 

[Bettalover333]

Update:

I went ahead and got an API Master Liquid Test kit to check my water levels, and it turns out i have very high Nitrates. (Ill try to include a pic below) Any suggestions as to how to lower them? Do water changes help? I think I read somewhere that high Nitrates make fish more susceptible to illnesses, is that true? Perhaps that is why this mysterious black spot appeared. Sorry there are so many questions, I'm new to the fish world and don't know a ton. Thanks for any advice you can give.

 

[Bettalover333]

Pic of Test results

Sorry i don't know how to upload pics. Can someone explain please?