oxygenating my new tank

my new tank is a 120l 60cm cube with a fluval 104 canister filter.
it currently houses some glowlight tetras and one CAE.

the filter's intake is on the back glass on the right-hand side of the tank and the outlet on the back glass on the left side of the tank. the outlet is just a nozzle, no spraybar or anything. it's near the water surface so there is quite a bit of surface agitation and it points towards the front of the tank.

is this adequate to oxygenate the water? or will I need to add any other equipment?
I've had a couple of the tetras die during the last few days (they were gasping near the surface shortly before death).

I bought the tank from somebody (cycled, mature media with all current fauna and flora as is) and its been running with me since friday. We performed a +- 50% water change when setting up the tank at my place and I did another 20% wc 2 days ago after the first tetra died.

unfortunately I dont have a test kit (yet) so cant tell you what my water values are.

 

As long as there is surface agitation, your oxygen should be fine.

I think you should buy a test kit for Nitrite, Nitrate and Ammonia and test. You might have had some bacterial die off, causing a new cycle to take place. But you really would need to test your water parameters to be sure.

When you did your water changes, did you dechlorinate the water before adding it to the tank?

 

slagter, yeah, thats what I thought, mini cycle, hence the water changes.
I'll get a testing kit ASAP. and yes, I did dechlorinate the water before adding.

if I reduce the filter's flow (I plan on adding some dwarf gouramis at some stage) will I still be ok oxygen-wise?

 

As long as there is some surface agitation you should be fine. When you do slow down your filter, make sure you slow down the return to the tank. Otherwise you could damage the canister filter pump.