removing rotis and ciliates from microalgae culture

[Bob Williams <williams at 99main_com>]

A splash of water, a few bad assumptions, and I recently found my entire 
saltwater micro-algae culture wiped out by a rotifer bloom.  I'm bouncing 
back, but seem to have some ciliate contamination which, if unchecked, could 
be just as bad in time.

Yes, I will go back to carefully maintaining a couple clean tubes of algae. 
And yes, I can always get more starters.  But it got me thinking.  Is there 
anything commonly available that is 1) selectively toxic to marine 
zooplankton such as rotifers, ciliates etc... but not to phytoplankton and 2) 
short-lived, so that the water would be cleared of zooplankton, the algae 
will keep growing and can then still be used to feed zooplankton after a 
period of detoxification?

An article from the Artemia Reference Center mentions using CaO to raise pH, 
or a combination of urea and hypochlorite, or possibly rotenone for killing 
larger predators.  I don't know how effective they will be on rotifers and 
ciliates since rotis seem to tolerate higher pH and eutrophication conditions 
better than, say copepods.  The rotis could be fed to delicate creatures, so 
I can't have any residual toxicity.

So far, I haven't had much success finding a mechanical filter that will pass 
something like Isochrysis and not also pass roti eggs.

Suggestions?

Thanks,

Bob Williams
williams at 99main_com