Please help 1 death already

[NuggetChops]

Air pump turned off last in prep to add my new co2 diffuser woke this morning to all my fish gasping at the top and one death. Co2 not even added yet

Checked ph and ammonia both find. Nitrates slightly high so doing a water change. Assuming it today with the air pump and lack of o2 but why air pumps aren’t necessary are they? What should I do. I’m wanting to add co2 diffuser. Fully planted tank a lot of plant. I don’t want to harm the fish.

Please help.

 

[GaryE]

What size of aquarium and what fish, species and numbers?

For now, a water change, but how large a change depends on how often you normally do routine water maintenance.

Have yo added new fish recently (coincidence could be at play)?

 

[MattW]

What filters do you have running on the tank? I found If the waters surface tension isn’t being broken, gas exhange levels aren’t as high. When I set up an old tank my old ember tetras had similar behaviour to your fish until I moved the filter outlet towards the waters surface.

I agree on a WC as well just to be safe.

Another thing to add is that the plants will also impact levels. During nighttime they will absorb oxygen rather than producing since photosynthesis isn’t taking place. The O2 levels for fish won’t be as high during the night.

 

[NuggetChops]

Hi sorry 120litre tank Approx 1/3 water change weekly.
I have ef-250 pipe is submerged I was thinking about raising it to add aeration but it saying the joint has to be submerged so not sure if that is possible.

I have:
4 Cory
4 rummy nose
1 rainbow shark
5 scissor tail
5 Buenos Aires tetra
4 dwarf rainbow fish
4 oto carfish

No new fish added recent I feel I’m at max capacity.

So I did a 50% water change. Put air pump bk on for couple of hours fish have settled returned to normal. I have added co2 diffuser after that it’s on a timer so will turn off around 6pm and air pump is now on a timer and will kick in after co2 if off and through the night before diffuser comes bk on. This seems to be ok so far fish are all acting normally.

Phosphate ate high so ordered some seachem
Phosguard which I will add to filter tomorrow when arrives.