Hellp Red Devil

[reddevil12345]

hi, i have a red devil it is about 3 years old, i moved it from a 4ft tank to a 2ft, it was behaving excellent in the 4ft tank with no problems. but now in the 2ft tank
it hasnt eaten anything for more then 3days,
its very agressive,
tries fighting its reflections,
it has a dark black patch on the chin and goes upto the belly,
it keeps going to the back and shaking alot which makes the sand go everywhere,
it ignores all the food like it cant see it and its very active all day. whats wrong ? i used like 3-4 lites of the old water and same filter and heater.
i think its female as it dont have a bump on the head, and its alone in the tank (has been alone for 3 years)

plz help

 

[WILDER]

Can you post water stats in ammonia, nitrite, nitrate, and ph, as black patches can be ammonia burns thats are healing.
Look under black patches.
http/www.fish-disease.net/diseases.htm

 

[FISH KEEPER EXP]

what are water stats?
also how big is the red devil, they get stressed when there is not room in the tank?