Hello!
I have a year old 5 gallon fish tank. 2 platys , 2 longfin danio and a little catfish type. Tank is great no issues but out of nowhere one platy started showing signs of distress. Test strip showed moderate nitrates and nitrites but not high. Did a water change last week. Platy looked great after was back to old self. But now a week later today she’s dying. Water strip is about the same read again now. I do water changes about once a month maybe every 3 weeks and use Seachem prime and stability. Have a black coarse pad filter with white fine pad in front and just change the white pad maybe every two months. Haven’t had any issues in a year since its cycled. How can suddenly I start having these issues? No other changes to the tank.