Sunburst Platty Black Spots

[leykis101]

I'm a newbie with fish and don't know much. I have a 5 gallon fish tank with 3 sunburst platties, i've had them for about 1 month. I've recently noticed that all 3 have black spots on the top. Specifically, between the top fin and their eyes. I took a picture which you can see here http/i153.photobucket.com/albums/s208/nailbomb2/Snapshot_20110509_3.jpg
I have a filter and keep the heater at 79. I feed them 2 or 3 times a day through a 5ml 1 teaspoon of TetraMin and everytime I change 1/4 of the water(every sunday) I use StressCoat+ which i bought from PetSmart. Why are these black spots appearing? Thanks in advance.

 

[soybean]

It's hard to really see on that photo but you should do some large water changes, at least 50% a couple of times a week, as it may be a problem with your water quality.

It's good you have a filter but I'm going to assume you didn't cycle it first? There are endless threads on cycling filters here, have a quick search.

Do you have a water test kit? You need to test for ammonia, nitrite and nitrate.

On another point, you're feeding them way too much imo. This is probably contributing to poor water quality.