I set a 60 litre tank up and run it for 3 weeks, all water parameter levels fine. Added 4 fish, left 4 week's all fine. Added 4 fish again and 5 days later fish started to die. Checked levels and the nitrite and nitrate were totally soaring. After first fish died on Saturday I did a gravel vacuum, large water change. Same again Sunday after another 2 fish died, also added Seachem Prime to try and save the fish.
Did another water change and vacuum today, still super high levels. I have 4 fish left and they are obviously struggling. I don't know what else I can do to help the poor things. I'm not very experienced with these problems, never had issues in the past.
Anything else I can do to help the poor fish? I feel so cruel 😥