Urgent help needed; nearly all fish dead and I have no idea why
#1
Tank size: 54l
Filter used: Marina i160
How long has the tank been set up?: A year and a half.
Water parameters:
pH: 7.0
Nitrite: 0ppm
Nitrate: 0ppm
Ammonia: 0ppm
Temperature: 26 degrees celsius.
Current population: 4 neon tetras, 2 amano shrimp.
The last water change was two days ago and I replaced 10 litres.
The tank was cycled and I bought the fish gradually, and chose fish which would live well together. The largest population was 3 albino cory catfish, 6 neon tetras, and 4 male guppies, but it took a few months to get there. There were no deaths for about a year and a bit, but a few months ago I started having deaths every few weeks. The most recent being I came home today and saw the last two male guppies had passed away.
We've taken action over these months such as more frequent water changes, monitoring the temperature more closely, keeping an eye on the water parameters, looking for signs of disease, removing plants when we thought they were causing too much debris, using filter-aid to boost bacteria, making sure the filter was maintained as well as possible etc. We spoke to someone in a pet store and they said it just happens and that it could be temperature related what with the heatwave. So the heater isn't on anymore.
I really don't know what to do. It wouldn't be so bad if I knew what was going wrong as I could fix it, but as I don't know I don't want to buy any more and risk more lives. At this point I'm wondering if it'd be better to just look after these tetras and shrimp the best I can and get rid of the tank afterward.
Does anyone have any idea what could be going wrong here? Thank you.