A few of my guppy babies in a well established tank turned nursery have started getting "saddles" as I call it. I've looked online all over for kinda sorta answers to what it is and in the mean time, they are starting to die. I treated with Melafix and Pimafix to no avail, so I've tried ich remedy. On those that have passed, some showed signs in the morning of the "saddle" and by evening they were gone. Since the two I've seen with the "saddle" have lasted a second day after treating for ich, I'm hopeful but it looks nothing like grains of sugar. It's slightly cottony I guess and they clamp their fins. I know I've not added all the info stated that's needed, but I can add if needed because I'm not sure on all that. The adults were moved to a bigger tank. This nursery is a 10g, live plants, tetra filter? (Came as a kit), weekly 25% water changes, age ranges 2 weeks to 1.5 months), heated.