Betta losing colour and behavioural difference

[pattyfurg]

So I have had my 20 gallon female sorority running for about a year
There were 5 bettas in the beginning but one died about 2 months ago, the sorority still ran well with everyone keeping to their territories and minimal-no fighting

Only this week has my lavender female started to show some signs of stress
- loss of colour
- not clamped but less showy fins
- stress lines
She also sometimes looks like she falls asleep at the top of the water and then suddenly wakes up and swims frantically
Iv watched her closely and none of the other bettas are harassing her
My tank is also heavily planted and has a small wall bubble filter
Iv done two water changes this week even though my ammonia, nitrite and nitrate is all 0
All other fish in tank are fine and active

The only difference I can think of is that she might have been able to see a male in a different tank and now he has been moved

 

[Delapool]

If you try a search, this sudden waking up has popped up before. I can't recall any details or cure unfortunately. Perhaps someone may know.

 

[pattyfurg]

Yeah Iv tried to search, obviously each circumstance is different and I'm looking for advice from people who may have experienced it