How fast can rotifers eat all the green?

What to do about a phytoplankton bloom?
The 150 gal tank was so green that you couldn't see six inches into it.
So we added a gallon of Suzy's rotifers. Four days later the water was still green. We were impatient. A filter sock was purchased and a UV Sterilizer was installed. On day 5 after the filter sock and UV were installed, the water began to clear. The sock overflowed within 24 hours. I wasn't able to closely examine the sock, but I saw some of the overflow residue. I believe it was clogged with millions of rotifers fat with algae. The algae is too small to have been filtered by the sock but when consumed in the gut of a rotifer 50-100 times larger, the sock did the job.

I still don't believe the UV Sterilizer had much effect. The rate of flow through a UVS is too slow. It's physically impossible for it to have had much effect other than to kill a few rotifers and algae before they were removed by the filter sock.

So I tried a little project.

A cup of rotifers was introduced into a gallon of my own special brew of phytoplankton. This is something that bloomed in my little jug all by itself, just from the same clean looking tank water as in the 150 above.

Days 1-3 saw vitually no change in color of the greenwater and no rotifers could be seen. On the fourth day I noticed a slight color change. Today is the fifth day and the color is definitely yellowing and rotifers are plentiful. Here are some pics:



The rotifers are easier to see with overhead lighting:

Mark Peterson wrote: I still don't believe the UV Sterilizer had much effect. The rate of flow through a UVS is too slow. It's physically impossible for it to have had much effect other than to kill a few rotifers and algae before they were removed by the filter sock.

I was talking with Ryan at Aquatic Dreams today, and he said that using an adjustable rate pump is useful with a UV unit.  He said to run it on a fast rate for algae problems, and a slower rate for ich problems.  Not sure if that helps, but it makes sense to me.  Algae multiplies at a fast rate.

Mark,

Let me know the next time you need to clean that filter sock. I'll come down and take a few million rotifers off your hands. Mine are growing --- but slowly!