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Re: green water

Roxanne Bittman wrote:
> What is really interesting about this is the variety of
> methods used to clear up green water, all of which
> seem to work, under at least some conditions.

I thought this very interesting, too and I think it reflects on the
complexity of the problem and on the diversity of our aquarium-keeping

> What else is curious is that, the day I posted my
> question, I returned home to the green tank, changed
> 25% of the water, added no fertilizer, added 2 capfuls
> of Kent's Pro Clear (a flocculent, tho' apparently not
> the best, see below) and three hours later, the tank
> was crystal clear.  Not just better, but eye-poppingly
> clear.
> I was surprised, since I had done exactly this set of
> things twice before, with no such result.  I must have
> hit a threshold of nutrient lack and low algae (Euglena,
> I am told) population, so that the flocculent did its job.

This is somewhat like my first experience with Hagen's flocculent "P
Clear".  The evident difference being that my first application had some
effect but left the tank still cloudy.  The second application worked
perfectly.  I reasoned that there was so much algae in suspension during
the first treatment that the flocculent got "used up" before it effected
all the algae. The second time there was less algae there and enough
flocculent to handle it all.

There are a lot of different planktonic green algaes and cyanophytes that
might cause green water.  That diversity could be one reason why Roxanne
got so many different answers about how to clear up the problem.  Euglena,
for instance, can't use nitrate as a nitrogen source but most other plants
and algae can.  Adding nitrate would feed everything in the tank *but* the
green water and hand the competitive edge back to the plants.  Other
people have reported that fine filters alone will pull down green water
blooms, but that didn't work for Roxanne and it didn't work for me.  The
failure would be explained if the algae species that didn't filter out had
a smaller cell size than the algae species that could be filtered out.
Adding a flocculent overcome's the cell-size problem.

In my tanks I get green water mostly when I do something that slows down
the growth of the plants without reducing the light or nutrient levels.
That's usually heavy pruning, thinning or replanting.  When the plants
slow their growth the single celled algae are the first ones to take up
the slack.

I suspect that other people have similar experiences; green water blooms
happen when something slows the plant growth or there's a sudden increase
in the light or nutrient availability that shakes up the balance.  The
wide range of solutions reflects the many different "balance points"  that
different aquarists maintain and the many different ways that the tanks
can get knocked off from and returned to their balance.

Roger Miller