Is this fin rot?

[chibifish]

Hey guys, noticed Shinji had some torn up fins (the top fin mainly, and a little bit of the bottom fin) with a grayish/black on the torn parts. Think it's in rot? And if so, what should I use to treat it? Here's the info-

Housing
What size is your tank? 10 gallons
What temperature is your tank? 78*
Does your tank have a filter? Yes
Does your tank have an air stone or other type of aeration? Undergravel filter using air stones
Is your tank heated? Yes
What tank mates does your betta fish live with? None

Food
What type of food do you feed your betta fish? Aqueon Betta Food
How often do you feed your betta fish? 2 in the morning, 2 at night

Maintenance
How often do you perform a water change? 1 - 2 weeks
What percentage of the water do you change when you perform a water change? 10 - 25%
What type of additives do you add to the water when you perform a water change? Prime and Nutrifin Cycle

Water Parameters:
Have you tested your water? If so, what are the following parameters? Yes, just now before the water change

Ammonia: 0 ppm
Nitrite: 0 ppm
Nitrate: 5.0 - 10 ppm
pH:
Hardness:
Alkalinity:

Symptoms and Treatment
How has your betta fish's appearance changed? Top fins have started to look frayed and torn, with some grayish/black around the torn part
How has your betta fish's behavior changed? Not at all, still eating and flaring and swimming around like normal
When did you start noticing the symptoms? Today
Have you started treating your fish? If so, how? Water change and added Stress Coat
Does your fish have any history of being ill? No
How old is your fish (approximately)? Got him on September 28, 2012. Not sure how old he was when I got him

Here's a picture of him before:


And here's a couple pictures of him now:

[shellieca]

I would suggest doing more frequent water changes. I do weekly 50%+ water changes in my tanks. 10-25% every 2 wks isn't sufficient, IMO, even though your water tests are good. Keeping the water clean is going to be the best medicine & the best way to keep it from getting worse & maintaining his health long term. Many will suggest adding IAL & Aq salt, I just use fresh water & that works for me.

[asukabetta]

+1 make sure that it also isn't fin damage from tail biting or things around the tank like filters and ornaments. Those injuries + dirty water lead to fin rot as well.

Adding a bit of Aq salt for 10 days will help you too, 1 tsp per gallon.

[chibifish]

Okay. I thought a 50% change would upset the cycle? Plus, the water tests were good and there's no food that falls to the bottom. Thanks for the help.

[Tikibirds]

I dont know about under gravel filters but with the other filter types, the majority of the bacteria is in the filter itself and not in the water column so a 50% should not hurt the cycle with those kind of filters but I have NO idea how under gravel filters work so it might be different.

Since he is the only living thing in a 10 gallon tank, 25% water change a week should be fine. I do more because I have snails and plecos in my tanks and they poop too damn much.

If he does have fin rot, it would be easier to treat him in a smaller tank because for that you should be doing 100% water changes-especially if you are going to use aquarium salt. You don't have to but alot of people recommend it. it would be 1 teaspoon per gallon. Make sure its disolved before adding in the fish and you shouldn't use it for more then 10-14 days.

according to aqua advisor you only need to change 5% of the water per week for one betta in a 10G