I am a new aquarium owner and have had my fish for less than 2 weeks. A few days ago I noticed one of the female Mollies was swimming at the top and was not active she started to get white marks around the mouth. I tested the water and the nitrate was very high and performed a 30% water change to help it. That night the molly died i have tested the water again yesterday and its looking alot better.
The issue being that this all happenes in 24 hours, the fish seem to be fine then they just seem to lose all energy and within 24 hours they die. As soon as one dies another one gets the symptoms I have lost 2 now and another one is pretty bad I need advice and fast... Why are they dropping so fast? how can i stop it?
The healthy fish have no marks around their mouths and no marks on the bodies of the fish.