My catfish keep dying - plz help!!

[Sabzlike]

Please help:

I am new to the hobby. I have the fluval edge 46L tank.

Water perimeters are:
Temp: 24.5
PH: 7.6
Ammonia: 0.25
Nitrite: 0
Nitrate: 2

My substrate is black small Gravel but they aren’t polished / super smooth. Thank is planted with decorative rocks.

I have 10 cardinal tetras since the beginning months ago which are healthy.

I had four corydora juliis, three of them died after a couple of weeks. I had two Venezuelan corydoras, one of them is dying about a month after purchase. The fish is on it’s back and struggling to breath and has lost colour.

I am feeding a small pinch of flakes for the cardinals and one wafer per two catfish once a day.

I have also had three hillstream loaches die in the past.

I can’t figure out what the issue is. It’s incredibly sad to see them die without a clear reason. Would be grateful for your advice.

Generally my catfish are very docile and passive. They mostly sit at the same spot all day so I wonder if they don’t like my substrate.

 

[Aiken Drum]

A 46 litre tank is too small for all those fish. You should look at fish more suited for your tank size or get a bigger tank, say double the size of what you have.

What is your normal water change schedule? Im very surprised you are able to maintain those water parameters with all those fish in that size tank unless you are doing very big, frequent water changes. So, i would question if you are doing the testing correctly. Especially the nitrate test. What test kit are you using?

Corys do better in groups. Keeping a few more corys in a larger tank may help. Keeping them in small numbers in cramped conditions is stressful, and stressed fish suffer from ill health and shortened lifespans.

Are they getting enough food? What kind of wafer is it?Algae wafers isnt a very good diet for them as Corys arent algae eaters. They will have a go at it if they are hungry, but they need a more balanced diet. Is some of whatever you are feeding the tetras getting to the bottom for the corys to forage for?

Does your aquascape provide plenty of hiding spaces for the corys? They like to hide in little caves, in and around pieces of driftwood and plants. Again if they arent comfortable they get stressed.

Gravel isnt always a good substrate for corys. If it has sharp edges it can harm their barbels. Are you seeing any deterioration of their barbels?