Urgent Help Needed

[TekFish]

I have had a load of fish die off, a BN catfish, Apisto agasizzi, a rummynose, many neons. Have checked ammonia, nitrIte and nitrAte, all 0. All of this happened within a week and I have no idea what's going on, help? No symptoms, no bloating, flashing, heavy breathing, nothing. So confused. 

 
Tek oot.

 

[mark4785]

I have had a load of fish die off, a BN catfish, Apisto agasizzi, a rummynose, many neons. Have checked ammonia, nitrIte and nitrAte, all 0. All of this happened within a week and I have no idea what's going on, help? No symptoms, no bloating, flashing, heavy breathing, nothing. So confused. 

 
Tek oot.

 
Nitrates are rarely 0 ppm unless you have a planted system where the plants absorb it up quickly to grow. 0 ppm of nitrates can be indicative of an aquarium that doesn't have any nitrobacter or nitrosomonas bacteria which collectively convert ammonia and nitrite into nitrate.
 
Did you do a fishless cycle on the aquarium before adding any fish?
 
Do you have good water surface agitation? It could be that there is a lack of oxygen getting into the water.

 

[TekFish]

The tank has been set up 6 months, yes I did a cycle and I have a heavily planted set-up. Oh, and I have an airbrick.
 
Tek oot.