Help, crisis in nursery tank 😩
I have a little 15 litre tank with 2 week old molly fry, I set it up just after they were born and used the inlet sponge cover from my main tank to seed the little filter that came with the tank, it was otherwise bare other than the heater. It was fine for a few days then a couple of fry died, I’d been testing every day but on the day I discovered the deaths the ammonia was up to 0.5. Did a big water change and all was well again. Anyway yesterday I decided to put some plants and gravel in there so I could have some of my blue shrimp in there to help clean up. I rinsed the gravel thoroughly first and did around 40% water change when I added it, fish all seemed happy enough. Today I found 2 dead shrimp and another dead molly, the rest of molly and shrimp were all hanging out at the surface. I tested for ammonia and it’s still 0, but then did nitrite and nitrate test and got a big shock, nitrite test went bright purple so 5.0 ppm , nitrate either 40 or 80. I don’t know what happened, could it be the gravel? I thought adding plants from main tank would aid filtration not mess it up.
I’ve done a 50% water change and fish are all swimming around again so seems to be ok for now but I’m worried, I don’t want to lose any more fry.