I have had my 55 gallon freshwater set up for about 4 - 5 years now.
It's mainly been used as a female betta sorority, so it's filled with rock caves, driftwood, and java moss. There were 5 female bettas, 2 dwarf sunset platys, 3 mollies, and a leporinus fasciatus. All have been in this tank for 6months to a year, except the leo - he was added about 3 months ago (never aggressive towards my other fish, and only about 3inches long-had plans to rehome him once he grew, was quarantined before placed in the tank).
I noticed about 2 weeks ago that my leo and my platys were getting ich, so I bought some rid-ich and treated the tank.
4 days ago my molly gave birth to about 30 fry. Most were still born, several were deformed and so I culled them, and the rest are HUGE for molly fry. They seem to be about the size of month old fry.
All fish were alive and well until yesterday. The mother molly was dead as well as one of my female bettas. I did a 25% water change and gravel vac (I was due for my weekly change anyways) and added some aquarium salt (can't think of the exact amount I used, but it was per the directions I have always used in the 5yrs I've had this tank.)
As of this morning ALL of my female bettas were dead and the remaining mollies, platys, and leo are at the bottom of the tank and not really moving.
I can't say that I found anything physically wrong with any of the fish, however one of my females appeared to be literally missing scales from around her face - she was in a breeder net because she didn't look well last night, so I know the other fish weren't munching on her.
amonia - 0
nitrite - 0
nitrate - about 10ppm
I know it's not something wrong with my water or dechlorinator as my bettas in smaller tanks are perfectly fine. Could it have been the rid-ich? Anything I can do, or are all of my fish doomed to die?
Most of the fry have died off as well. I originally had over 30-I'm down to 12 now.