Algae in the fishtank - Whatever shall I do?

Ian Russell Ollmann iano at
Wed May 4 20:20:07 EST 1994

I have cultured some rather tenacious green critters in the living room fish tank. The
usual clumpy green stuff is nicely done away with by my rather fat and happy plecostomus
(sp?). No, No, that is not the problem. Rather, the tank is now plagued by single-celled
algae which renders it a lovely cloudy green. Sadly for my algae eating fish, there is no
clumpy matter to eat. The water just appears green. This is not good for seeing fish, so
I decided to take action. So what did I do? Being a chemist, I naturally resorted to
chemicals first. I purchased something called Green Water which (contrary to what one
might think from its name) is supposed to clear up water. It didn't. It didn't even at
nearly twice the recommended dosage. I tried restricting light to the tank - the lights
have been burned out for a month - but that has not fixed the problem. I did the usual
change the water thing repeatedly and even resorted to buying one of those aquarium
vacuum things to vac out the crud from inbetween the gravel. The tank was even nice and
clean looking for a day, but has returned to its usual translucent green three or four
days later. In desperation, I took a sample into the lab and took a look at it under the
microscope. What I saw were a bunch of non-motile, single-cellular, green helices which
wind for exactly one turn and then stop. I don't suppose anyone has any suggestions as to
what they are (genus-species) or how to get rid of them in an inexpensive fashion. It has
already been determined that a minute in the centrifuge gets rid of the stuff, but that
is not fish friendly, and I don't have enough funds to purchase a flow-through centrifuge
to replace my aquarium filter. 

There are a few more bits of data which may or may not help. This happened once before
last August and the problem eventually went away after two months, apparently on its own.
I added freeze dried drosophila as a fish food for a few weeks before it cleared up. It
may be possible that some survived the freeze-thaw process and the hungry fish to help
defeat the horrid helices. Unfortunately, I didn't run a control with an identical fish
tank, so I can't establish any cause-effect relationship. Addition of what drosophila I
had left didn't seem to cure the problem this time. Oh yeah, the green stuff goes right
through the existing aquarium filter. Changing it hasn't helped. I don't think I can get
enough flow through a 50 micron filter to warrant bothering with that. 


				A weekend fish enthusiast. 

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