We set up a 10g tank on Saturday, using all the gravel, filter, water, etc from a fully cycled 5g tank, and topped up the water with tap water treated with Prime. Tested the water : 0 ammonia, 0 nitrites, 10 nitrates (our tap water reads 5 nitrates as is). Added 3 mollies - 2 females (Salt and Pepper) and 1 male (Spot), and a few ghost shrimp. Sunday, noticed a few fry (about 1cm each). Monday afternoon, we noticed that Pepper was lying on the bottom of the tank. Breathing, still moving about a tiny amount. Monday evening, she was swimming after some food. This morning (Tuesday), she was dead I took her out, did a water test (ammonia <0.25; nitrite 0.25, nitrate 10) and changed out 50% of the water, added a little extra Prime. The male and other female, and the fry all seem to be moving about okay, though I admit, I'm worried now.