rotifer cultures contaminated with something...

[flipteg]

my rotifer cultures are contaminated with something but i don't know what they are... they are much smaller than rotifers and they swim a little faster than rotifers... they swim in a smooth motion unlike the jerky movements of copepods... under the microscope they look like little oval eggs... they are out competing my rotifers for the phytoplankton and they are wiping the rotifers out... any ideas what they could be...?

[flipteg]

after some research on the Internet, i am now fairly certain that the problem are ciliates... nearly wiped out all of my phytoplankton cultures and had to restart the rotifer cultures... bought bleach and soaked everything that comes in contact with the water...

the question is, does anyone know how it got there in the first place...? my phyto cultures has been going for 6 months now... rotifers for about 6 weeks... then all of a sudden, total wipe out...