Is this fin rot or a torn fin??

Hi,
I noticed yesterday that my betta fish wasn't using his left fin to swim and was only using his right fin. This morning I noticed what looked like a small split in the fin and after having come back from university today it has gotten significantly bigger.
As far as I can see, it is only the one split although it is hard to tell as when he comes out he is moving around alot still. He is eating well and still comes up for bubbles etc. His other fins are in good condition with no tearing showing. He is also making good use of all of them bar the left one.
Water Paramaters are as follows:
Nitrate: 10mg/l
Nitrite: 0mg/l
Ammonia: 0ppm
PH: 7.6
Temp: 25.5 celsius
He's had a water replacement & filter clean in the last couple of days and I also added some general tonic when he first starting clamping his left fin in case of bacterial infection. In terms of his tank decorations, he has some gravel and the bottom, silk plants and a wooden log (also at the bottom). He then has a floating fake hollow log which he sleeps in. There is also a leaf in there for tannins that he likes to sit under ( I think it was an almond leaf but my girlfriend was the one who set it up ).
His only tankmates are two amano shrimp.
I think this is all the info but if there is anything I've missed let me know.

 

I'd say it looks torn, but hasn't started rotting.
It doesn't sound like there is anything in the tank that he could have torn it on, but you could run your hand along the inside of the log, and see if there's any sharp bits.
I'm not sure about the amano shrimp, but I don't think they would attack him.
I'd say clean water, and finding the cause, is probably the best way for his fin to heal.

 

Hi and welcome to Fishlore!

That is a beautiful betta boy!!!

Bettas are also known for trying to fit into small places, too. I have had more than a few long finned bettas split their fins while trying to squeeze behind the heater in their tank. Just something that you might look out for...

ForBettaorForWorse is right on....frequent, small water changes, like maybe every other day for a little while, ought to help that fin heal right up!

 

A little stressguard added in may help promote healing and growth, but my experiments haven't convinced me. The clean water is the important part.

 

Definitely a tear.

 

It's for sure a tear. As said above, look for sharp things and small spaces. Make sure the tank is clean so it can safely and quickly heal. I don't know if Bettas can nip there, but fin nipping is another possibility, so look out for that as well (though I wouldn't stress it too much).
He seems super healthy. I can't say for sure, but he looks show quality!