Daphnia From Bare Tank, How Is It Possible? Options

[desireless]

I found my fishes in my main tank displaying some signs of gill infection. So without further ado, I hospitalised them in my QT tub. The tank was left fishless but the sponge filter still run. PL lights running on timer also operate as per normal because I wanna keep my wall algae.

Today, which is the fishes' 5th day in QT, I found some organism developed at the surface. On a closer examination they looked like Daphnia. It is different from those I bought from LFS. I assumed that these are Daphnia based on theire behaviour. Those I bought from LFS are pinkish and roundish. But these I found in my tank are longish and orangy in colour...



Direct Link: http://www.rafflesgold.com/desireless/MOV06310.wmv


How is it possible that Daphnia can developed from a tank which was started from bare? In between I've fed my fishes no Daphnia. Only live food which I feed them are the bloodworm cube... are they responsible for the developement of daphnia too??

How come my tank always come with live oraganism? There was once live bloodworm, then Planaria. Now having removed fishes frm my tank, it is infested with planaria and daphnia