Overstocked that why they are getting ill.
The filter not coping with the load of fish in the tank.
Is it possible to buy a bigger tank for them.
Danio are active fish and shouldn't really be nkept in anything less than a 20 gal.
The same with the glowlites active fish and need no less than a 10gal.
To be honest not one fish should be in that size tank.
Mine twitch there fins.
Plus your nitrite reading not 0 so it will be irratating them.
The filter not coping with the load of fish in the tank.
Is it possible to buy a bigger tank for them.
Danio are active fish and shouldn't really be nkept in anything less than a 20 gal.
The same with the glowlites active fish and need no less than a 10gal.
To be honest not one fish should be in that size tank.
Mine twitch there fins.
Plus your nitrite reading not 0 so it will be irratating them.