So, I just started my aquarium. Water temperature is about 79 degrees (goes down to 76 in the night though). I added four von rio tetras (about an inch long apiece) and let the tank sit for three weeks with them. Added three plants (a crispus, anubia, and a chilensis), and waited another two weeks. So it was five weeks from the start. I had the water tested weekly until this five week mark, when I saw there was no ammonia, nitrate, or nitrite present in the water. The cycle was done (said the person in the aquarium store), and I could put more fish in. So here's what I added. For those of you who read my intro, I just got out my list of their names):

1 Yo-yo Loach
1 Dwarf Frog
1 Bushynose Pleco
2 Panda Corys

So that was last Saturday. They all seemed fine. I feed once a day in the afternoon. My tetras always eat (I give them one flake each), the loach is digging around on the bottom and must be eating *something*, and the pleco is eating algae (I think). I haven't been able to observe the corys or the frog eating, but that doesn't mean they aren't as soon as I turn my back since the food disappears. I also drop in some frog food for the frog in addition to the flakes.

Yesterday I noticed a white blotch on the side fin of one of my corys. I didn't know what it was, so I left it alone for a day to see if it worsened. I just got home from class and that cory is dead. Now the other one has a whitened (but not a distinct white colour) patch on the scales where the adipose fin attaches to his body. I'm concerned.... I don't see myself as having done something wrong (please let me know if I have), and I wasn't aware that an illness could kill so fast.

One thing I do notice is one of my corys would swim around a lot, swimming against the sides of the tank, and crazy. The other is much calmer. I'm not sure which one died, because I can't tell them apart easily....

Can anyone shed light on the subject? If pictures would help I could give it my best shot (which isn't much.... no good camera). Really sorry for such a long post; I know it's a terrible way to make a first impression here. I'm just clueless. As far as I've been told, there's no "Read this book to become a total expert on fish care" book.