In a 30 gallon aquarium that's been up for 3 weeks, and just got through cycling, about half the zebra danios suddenly got really bloated looking. The fins don't stick out, but their belies are FAT. We had an ammonia and a nitrite spike, cured by daily 40% water changes a week ago. Now water parameters are almost perfect with almost no ammonia and no nitrites. Their gills just cleared up from being quite red. As I said, the danios are the only ones that appear affected. I already removed all of them from the tank...I'll surely get flak for this when my girlfriend gets off work... But the corys, 2 green 3 peppered, 2 sterbai and 3 bandit all seem pretty happy and active. Honestly I have no idea what made the danios bloat. What should I do? I read to raise the temp to about 78-82, seems harmless.