Black Ghost Knife Erratic Behaviour

Hi,
my black ghost knife fish is approx 5 years old, and has always lived in a community tank. In the last 4 months or so, he/she has started being very active at the top of the tank, even swimming vertically with about 1/5th of his body out. He/she has even made contact with the glass lids.
Nothing has changed recently, still doing weekly 1/4 tank water changes, temp is steady at 25c, and ph sits close to neutral. Feeding twice a day with frozen blood worms, sinking pellets or flake.
I'm only going to take a guess, but maybe he has suddenly noticed his reflection ? Maybe becoming sexually mature or territorial ?
There's a pic attached, hopefully it works.

thanks !

Tank stats may help figure out behaviour

Yes; tank size, tank mates, plus full water stats (ammonia, nitrite, nitrate, hardness), if you have them, would help us a lot.

A consideration with BKGs and erratic behavior is it may relate to stray electrical current in a tank. These fish have a weak electrical sense which can be disturbed by stray voltage or similar electrical considerations.
 
Another thing to check is water quality. They are especially sensitive to poor conditions. I would suggest you increase the amount of water you are changing weekly from 25% to at least 1/3 and 1/2 would be even better.
 
Finally, I see you have clown loaches in the tank. Clowns like to hide in similar places to the BKG, so perhaps there is something going on in this respect.

Have you added any new elements to the tank recently? Like salt? Fish like black ghost knifes are very sensitive to salt. Other than that the other info would be useful

4ft x 1ft x 1ft tank
Tank mates - 5 clown loaches, 3 silver dollars, one dwarf gaurami, one skull creek rainbowfish. All from start.
PH - 6.6
Nitrite - 0ppm
Ammonia - 0ppm
Nitrate - 0ppm
No new medication / salts etc.

Tried turning heater off but no change (stray currents)

Is there a lot of water flow? He/she may be trying get air...
 
In the end there may be nothing wrong with it, my L25 pleco was acting similar to your black knife not to long ago for a few weeks but is now acting normal, maybe breeding season and is now sexually mature? 
 
I would also recommend upgrading the tank to a 125+ gallon, as these guys love to roam around at night and like the extra room to turn etc...