Hello, looking for some advice please as don't know what to do!
Established for 6 years
Recent stock - 2 goldfish, 1 plec, 2 danio, 2 minnows
All have been living in harmony for at least 6 months. Have been doing regular water changes every other month. Due to ill health and a long spell in hospital I hadn't managed to do a water change for approximately 5 months until 3 weeks ago. I checked the water levels prior to the water change and the nitrates were quite high. After the 50% water change I continued to check the water on a weekly basis and the nitrate level did not drop. I then did another water change two days ago and discovered that one goldfish and one minnow were dead. The plec was also looking weak. Tonight the plec died and after checking the water levels again, the nitrate level is still high!
I just don't know what to do. In the 6 years I've had the tank everything has been healthy until now.v
Thanks for reading.