Fish Are Going Berserk

[twintanks]

The peace of my new tank is now shattered. I offered up the morning feed today, switching on the tank light to find my six neon tetras belting around and pursuing each other, with duels every few seconds on the castle ramparts and behind the plants. Also my blue dwarf gouramis' behaviour has changed; whereas before,they seemed to be feeding together fairly peacefully, the striped male is now bullying the ?female/male (another post under Gouramis elsewhere re gender) who now spends quite a bit of time hiding inside the stone castle.
This does not seem to have been caused by any one particular factor; the water is ok (0 ammonia and nitrite, 5 nitrate). The tetras' change of behaviour is quite sudden, they are now swimming singly and not in a group. The gouramis have been playing up for several days now.
The only other inhabitants are four cherry shrimp.There is no damage being done (i.e no slaughter).
(Tank 80x35cm, 90-100 litres).

 

[Byron]

How long have you had these fish?  I would suggest you are now seeing more normal behaviour.  Tetra live in shoals (large groups) and it is normal for them to establish an hierarchy; but what you have described could also be the initiation of spawning, though more likely just "play" which to the fish of course may be more serious than play in our sense.  As for the gourami, males are territorial.  Rivals can be hounded to the point of death.  And it is not uncommon for females to be similarly treated especially by an overly-dominant male.
 
Byron.

 

[twintanks]

I've had them all for around three weeks now. The idea of it being more normal behaviour makes sense. I am new to dealing with this kind of fish; I've never had those problems with my goldfish. The ?female gourami seems ok but she must be a bit miserable being booted around all the time. There are no physical punch-ups but he/she is definitely the underdog.
Off to snoozeland now; any other thoughts welcomed.

 

[Byron]

I've had them all for around three weeks now. The idea of it being more normal behaviour makes sense. I am new to dealing with this kind of fish; I've never had those problems with my goldfish. The ?female gourami seems ok but she must be a bit miserable being booted around all the time. There are no physical punch-ups but he/she is definitely the underdog.
Off to snoozeland now; any other thoughts welcomed.

 
The neons are no issue, assuming I correctly identified what is going on.  The gourami issue though could be much more serious.  Only you can decide what if anything needs to be done, by careful observation.  The best way to observe fish is to sit in front of the tank absolutely motionless for at least fifteen minutes, preferably longer.  When I say motionless, I mean just that; fish can see outside the aquarium, and any movement by you will distract them (they will expect food, or whatever) from what they would get up to if you were not there.  If you do spot any interaction, remain motionless and see how far it develops.  Male gourami are territorial, some even as severe as male cichlids, and another male doesn't usually last long with some species, depending upon the fish.  Females are best in the ratio of two per male, though even this doesn't always work.  Constant hounding of the female will weaken her immune system (the stress does this), and sometimes death is not far behind.
 
Byron.

 

[RainboWBacoN420]

I've had a similar experience with my old 15 gallon. My dwarf gourami never bothered anyone directly, then I had a platy and a few guppies fighting, my gaurami came out of nowhere and started beating the platy like an old rag. Tearing some scales off and damaging one of his pectorals. 
My assumption is that the gaurami was influenced by the guppies picking on platy. Because before they never brawled or bothered each other at all.
Which could be why your gaurami is acting up, he sees your neons going crazy, which might have influenced him to act out like that.
The neons on the other hand, it's pretty normal, my neons do it all the time, and from close observations they're fighting over the females or establishing a pecking order. Then after a while they'll go back to normal, swimming together as if nothing happened. 
 
Are your neons still swimming around individually? Or do they eventually form a group again from time to time, if so, that's pretty normal behavior. 
 
Also, how is their color? Do they appear stressed and dull?