Over the summer I got an idea to set up a 5 gallon divided tank with all white on one side and black on the other. I finally got all that I needed, and when I added my fish to it, they got sick over night. They were lethargic and just laying around. I discovered that my heater wasn't working properly, so I took the fish out, and bought a better heater. I had 2 crowntails in it. One ended up dying shortly after and the other recovered. I don't think it was stress as I let these two see each other for a few weeks beforehand. So their tanks were right next to each other and they weren't stressed. I tried for a second time (with the better heater) and the same thing happened. This time it was with the same crowntail and a VT of mine. The heater was functioning perfectly.
Here's the specs-
Divided with a piece of plexiglass
Tetra HT10 50 watt heater (I use this in my other tanks as well)
3 plants on each side (plastic)
Bettasafe water conditioner
Homemade cave made of aquarium river rocks and put together with silicone
No water changes (both times the fish got sick in less than 24 hours)
The silicone used on the caves and holding the divider in place is marketed for bathroom use BUT says 100% silicone on it.
I use the same water for my other fish, and nothing has happened with them
the only other thing I can think of is that 4 out of my 6 plants I got off ebay. They were still in packages, unopened. but the packaging looked a little old. Like the plants were made a couple years ago. Also, everything was rinsed with hot water before use.
Any ideas on why this tank is killing my fish?
Edited to say, when I removed the fish, I put them in clean, heater water with some aquarium salt.