Betta Not Well

[AzyB]

Hello all,
i have a issue with my betta, two weeks ago i noticed my bettas fins and tail are clamped together so i did a bit of research and mostly found it was water temp. my issue is my water temp has not changed in 3 months so i did water changes every 5-6 days (25%) still my betta is not getting well. im new at fish keeping started 7 months ago and is my first fish to become ill.
his eyes are looking glazed and has a black lump on the left side under his gills which looking birds eye view of the fish is raised.

4ft tank
ph 7.5
nitrite 0.25
tank temp 26-28 oC 79-82 oF

fish symptoms: fins clamped together, glazed eyes, floating on top of my floating sheep 2-3cm below water surface, black lump under left gill.

Water change around 50% a month
other fish 2 beacon fish, 2 angel fish, red tail shark and betta

and help would be appreciated, thanks.

 

[phoenixgsd]

welcome to the forum, firstly your nitrite should be 0ppm anything over this is leathal, whats your ammonia and nitrate readings? your tank maintence could be more frequent maybe the large volume once a month is altering the ph in your tank and its a bit of a shock for them, you are using a heater filter and using a dechlorinator arnt you? could the injury be caused by agression in the tank?, angels, bettas and red tailed sharks are all agressive if not housed properly, i dont know anything about beacon fish so cant comment on those

 

[AzyB]

hi phoenix thanks for replying the nitrate is around 20-30 and ammonia is 0.25 0.50, i am using a bio life filter with heater inside and tetra aqua safe for dechlorinator.

the only argessive fish are the angel fish and betta, the beacon fish just hover around and the red tail just minds his own.
my other 5 fish are looking and acting healthy its just te betta.
thanks.

 

[phoenixgsd]

the ammonia and nitrite levels are too high, you really should be doing more frequent waterchanges, red tails often look innocent when your looking but can be killers, my mums killed alot of fish before we moved him