My Rainbow Fish Has A Growth Above Its Eye, Help!

I have a small rainbowfish in my tank that has a white-purple fungus growing around the top of its eye. Its eye isn't bulging, so I don't really think it's pop eye. I forget the full name of my fish but it starts with an f and it's a type of rainbowfish that is for smaller tanks. My tank is 10 gallons, I have the rainbow, a honey gourami, three pygmy corey cats, three cherry shrimp and a snail. My tank is well planted with plenty of driftwood and I do water changes every few weeks. I dose iron, potassium, trace and excel for my plants about every 5 days. I feed about every other day and switch off between small fish formula pellets and mysis shrimp. I use a sponge filter because I was told carbon filters could remove beneficial things for my plants. I've had my tank for about 8 months now and my water levels are as follows:
nitrates: 0
nitrites:0
GH: between 75 and 150
chlorine: 0
KH: 120
pH: 7
I use strips though, so they aren't totally accurate...

I'm worried about using antibiotics and salt... any suggestions on what I should do?
 
 

Am thinking your rainbow fish is Featherfin or Threadfin Rainbowfish, these are small fish.
 
Did originally sound like pop eye but if thats not the case then I will not be of much help am afraid 
Am afraid I do not know much abut illnesses in any fish.
 
Sometimes the trouble of using meds is they may do more harm than good if the diagnosis of illness/disease is not correct.
 
Also some meds are not good for shrimps and snails, so watch out for that.
 
So be careful and try and do a bit of online research to see if you can come across anything remotely similar and post on this thread and see if anyone will comment. Good luck.

No idea on the illness side, but could it be a forktail (furcatus) rainbow?
How often and what % do you do water changes? Have you added anything recently?
Can you get your hands on a liquid test kit, since the test strips don't test for ammonia & indeed are quite inaccurate?

Yeah its a furcatus rainbow! thanks! I ordered the drip test kits online, and so far the only ones that have come are KH and GH and those numbers were:
KH: 89.5 and GH: 161.1 and I subsequently added some neutral regulator to lower the GH. As for water changes, I usually do around 15-25% water changes and I refill it with half RO water and half tap with neutral regulator since the tap water where I live is really hard.

Sorry it took me so long to get the picture up! I had trouble formatting it to get the file size to be smaller!