protozoa in fish tank

Question
I have several 20 gallon aquariums in my Jr. High Science classroom. Yesterday I took several droppers full of water from under the gravel in one of the tanks to make slides for the kids to view using a microscope. We were all fascinated with the variety and numbers of microorganisms we observed in just a few drops of water. There were tiny ciliated guys zipping everywhere, small crawling worms, and larger worms with paired hairs on each section and a long proboscis, in addition to ostracods and others. Now I am wondering - are any of these guys harmful to my fish? Are they helpful? or just, well, there?  Should I be doing anything about this? I have guppies in one tank, platys and tetras in another, and crayfish in two other tanks.

Answer
Hi Shanna,
  As you have found out, any healthy aquarium will have a whole spectrum of different creatures in the water.  For the most part, this is perfectly fine.  If there are too many of some of these, it can be a problem, but on the other hand, having none at all can also be highly problematic -- fish do not do well in sterile environments.  I would leave them as they are and let your students enjoy all the little things that they can find.

-- Ron
   rcoleman@cichlidresearch.com
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