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Curing green water

Adam Novitt wrote about Green Water:

>One thing I've got to say is that from my very unscientific survey there =
>is absolutely no reliable cure for Green Water.  Some people do fight it =
>for months on end using magnum filters only to have it return in a =
>couple of days and numerous people have used the dark tank method to no =
>good end.  Many did massive water changes to nil results.  I think its =
>very safe to say that there is a great degree of variables here.

An approach that has worked well for me and a few others who have tried it
is to shade the tank with a floating canopy of Water Sprite or some similar
plant.  (One that grows fast, and grows rooted or floating.)  This counters
what seem to be the most common causes of green water: too much light,
excess nutrients, sparse planting.

The plants can be tethered in place by running a few threads across the top
of the water, secured at the edges of the tank with binder clips or
something similar.  Tieing individual plants is usually not necessary since
their natural buoyancy keeps them entangled in the threads. It's not a bad
idea to do a couple of large water changes during the process.

While waiting for the water to clear, try to isolate the original cause of
the problem.  (Too many watts of light per gallon?  Are there enough plants
in the tank?  Are most of the plants fast growers?  How long are the lights
on each day?  Has someone been leaving the light on at night?  Is the room
getting more sunlight than before, perhaps due to a change in season?  Has
the tank been over fertilized?)

Once the green water subsides, gradually thin the floating plant cover so
that direct light reaches the fast growing plants first, then the slower
growing ones. Use the excess floating plants to fill in any unplanted areas
in the substrate.

Ken Cova