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Re: Nitrates/green water/test kits (question)

David Brooks discussed his green water problems, To try to summarize,
filtering does not work; the green water comes back.  He plans to try
duckweed, next, then a Daphnia cage in the filter.

Daphnia cages work, but they are tricky to set up and you have to worry
about what type of screening you use.  They can work without any forced
water movement through them, but they should take up perhaps 10% of the
volume of the tank, and you have to have some snails inside and outside to
keep the screening from plugging up with algae.  Avoid window curtain
material!!  It is made of nylon threads, and these threads are made of very
many woven smaller threads.  The total surface area of nylon exposed is
great, and someting toxic is given off that will stop growth in your plants
in about a month and kill them by two months. This production of toxic
material will continue for years.  It is probably something released from
slow bacterial decompositin of the nylon.  Monofilament screens are safer.
If you have a current through the Daphnia cage, it should be a slow one or
else all the Daphnia will be pinned against the screening, and they can't
survive that for very long.  Daphnia cages work, but they require care and
patience.  Another possibility would be to have another tank nearby with
Daphnia and circulate the green water through this tank with an appropirate
filter to keep the Daphnia from being carried into your fish tank.

Water sprite seems to be better than several other plants I have tested in
keeping down green water.  Credit for the claim that water sprite is
exceptional, goes to Richard Sexton.  I did some experiments with different
plants to see how crowded they became before the green water went away.  In
the case of Hygrophila polysperma, Ceratophyllum demersum and Eigeria
densa, the tank had to become densely packed with the plant before the
green water went away.  I mean, packed so much that the resident guppies
had a hard time getting up to the surface to get at their food!  However,
with the watersprite, about half the tank could be open with light reaching
the bottom, and almost all the green water was gone.  There was only a
slight haziness.

For a quick but expensive solution to green water, try pumping the water
through an ultraviolet sterilizer for about four days.

Paul Krombholz, in hot, dry, central Mississippi