first of all is she eating?
is she active?
is she pale?
any strange behavior?
i need a bit more info
on another note,
i hate to be negative but do you have another tank or are you keeping all of those guppies in there?
red tailed black sharks should not be kept with any guppies or other "weaker community fish"
red tails are only community in very large, well planted/caved tanks
otherwise, as they grow older they become very territorial and aggressive, especially in such a small tank
and i was taking a look at your sig and i read that you are keeping several sharks in a 29 gallon
first of all, bala sharks will get to be around 14" and need way more room to swim
(like a 70 gallon)
secondly you said you are keeping a black finned shark,
would that be the black finned shark, AKA columbian shark, AKA shark catfish?
the columbian shark or "black finned shark" gets to be 18" and is best suited for a 100gallon tank
once again i do not want to be negative,
i am just helping you avoid disaster!
too small a tank will take a very harsh toll on your fish, shortening their life span and causeing lethargy and stress over time