I have a 20 gallon tank that has been established for about a year now. I have live plants, elodea and Java Fern
. The original inhabitants of my tank were 7 cardinal tetras, 1 Platy
, 1 Paradise Fish
, and 1 chain loach. Over the past 24 hours, all 7 of my cardinal tetras have died and just recently my Platy
Yesterday I noticed that a few of the tetras were swimming bizarrely, in circles, upside down. Then, they were just floating upside down although I could still see their gills moving. I did a 50% water change and used a double dose of Stress Coat. It seems after that then all of the tetras started exhibiting this behavior, and overnight they had all died. The Platy
in the past couple of hours was swimming sideways, then went upside down on the bottom of the tank and passed.
The loach has been hiding in a cave, but when I lifted the cave to find it, it looks very pale with tattered/translucent fins. I'm afraid it may go soon too. The Paradise Fish
is swimming regularly, but around its two side fins near the body it is very red, and looks as though it has a dark freckle near its head.
Here is what happened just before any of the fish showed any symptoms. The water temperature dropped down about 4 degrees F overnight (to 74 F) because I only had a 25 Watt heater. I bought a 100 Watt heater and put it inside the tank. The water temperature overnight arose back to around 78 F. That next day is when the tetras showed symptoms.
After I did the 50% water change, the water temp dropped down to 73 F, and with the heater it has since arose back to around 77 F.
I did a liquid test and the parameters are ammonia - 0, nitrite - 0, nitrate - 15, pH - 6.6
I just added activated carbon to the filter. It was previously running a sponge and BioMax insert.
Any help would be greatly appreciated so that I may save the lives of my two remaining fish, the Paradise Fish
and loach. The loach is not looking like it will make it much longer. Thank you.