What could cause open sore on my Albino Cory Cat?

[realj]

I have an albino cory cat that has an open sore by its mouth. It just appeared 2 days ago. It has like a hole in his cheek that has no color but pink inside. I have a 10 gallon tank with 2 cherry barbs, 2 neon tetras and this cory cat. I have had all the fish for 3 months now and the tank was cycled before they were added. As far as water parameters, I use API Freshwater Master Test Kit and tested Ammonia, pH, High Range pH, Nitrate, and Nitrite levels. The level results in my tank are as follows: Ammonia 0 ppm, pH 7.0, high range pH 7.4, nitrate 0 ppm, and nitrite 0 ppm. They are good levels according to the pamphlet that came with this kit. The temp in the tank is 82 degrees. I use Seachem Prime as water conditioner. I don't use aquarium salt. I am using Image Biosystem 15 power filter and a 4 inch air stone wand as aeration for tank.

I have a little decoration that looks like a little arch and on it are like little fishies and barnacles extending from it from little metal sticks. Well one had a turtle extended from it and somehow it got loose and came off. So for a day, I left that little metal stick, stick out until I noticed what the cory's cheek had and so I took it out and removed the stick. Now I don't know if it was because of this, maybe when he went up quick and came down quick maybe it caught him. I don't know.

Can anyone tell me what other things this may come from and how I can treat it? It doesn't look like he is in pain. Hes acting like normally and hasn't slowed down at all.

Here is a pic of my cat:
http://img61.imageshack.us/img61/7345/1002042oh6.th.jpg (http://img61.imageshack.us/my.php?image=1002042oh6.jpg)

Thanks in advance!

[fishorama]

Keep the water very clean, water changes every other day. Your temp is a bit high, lower your thermometer temp unless your in the heat wave we are. Watch for fuzzy whiteness, bacteria or fungus.

Is your tank newly set up? Zero nitrAtes are a sign of an uncycled tank unless a lot of live plants are present.

Once your cory heals & the tank is stable a couple more corys & neons would be good if you can keep up with frequent water changes, once or even twice a week. Your tank is small but both species need companions.

Good luck.

[pinkertd]

I agree, keep the water very clean and keep an eye on the sore. Definitely sounds to me like he got poked by whatever was sticking out. He may have darted into it. And 0 nitrates seems a little off to me too.

[realj]

I do a 10-15% water changes once a week. I thought that nitrates are better when it is lower? Every couple of days it goes from 20.0-0 (nitrates). Don't know why that could be.

Anyhow thanks for the suggestions. I am hoping it heals up soon.

[fishorama]

Weekly water changes should be more like 25-30% minimum. Until your cory heals do at least 20-30% every other day, shouldn't big deal on a 10g. Let us know how he does.