got 2 axies around 7mths old,both used to be very active and eat whatever is offered to them,now one has gone off his food and getting skinny,he went brown in colour (usually pink),now he is peeling and back to his normal colour ,temps ok and other test ok although ammonia a bit high,the other axie shows no signs of anything wrong,tank is 4ft long 18"high and 18" width,filter is internal and flows out at the top of the tank against the glass to mimimise disturbance,and sand at bottom,any help please:bowl: