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Green water: a cause?

One thing I have noticed in a number of tanks and in my own twisted
experiments with this alga(e) is that it is almost always accompanied by a
disturbance in the N cycle of a tank with a spike of NH4+ appearing in
almost every single case. Reasons for the NH4+ spike are many.

1)New tank-poor N cycle, not established yet

2) Filter removal, a spike since bacterial action has been removed/reduced.
We often see in non filtered tanks that slight haze or a continual issue in
high light no filter tanks.

3) Massive uprooting, removal of a small tree like sword plant etc (see
bacterial disturbance again). Messing too much with your tank in some way.

4) Nutrient removal-stunted plants not taking up NH4+ production and no time
for the bacterial responses. Turn off CO2 all of sudden, No NO3 etc. That
stops the NH4+ uptake that's taking place so it builds up slightly and
triggers the GW to propagate.

5) Other factors such as good growth then poor CO2 all of a sudden. Any
dramatic slowing of growth rates(hence less NH4+ uptake). Any event that
lets the NH4+ build up pretty much.

It seems that there a window of opportunity for GW that's in between the
bacteria getting it and the plants getting it. If care is taken to ensure
plants get fed well and that the bacteria have a good home as well(deep
sub's, wet dry filters, big canisters etc) this will minimize the outbreaks.

And water changes will remove build ups of NH4's so after a big hack, after
a long period of abuse, new tank set ups, good maintenance will take care of
your tank.

I do know GW water is not caused by: Most of the other nutrients. NH4+ is
the exception and the common issue in many experiences with to date. This is
how I induce it actually. I toss a couple of Jobes into the water column of
a very high light 20 gallon tank and it's there in a day or two. It will
live on little once it's there but seems to get "turned on" by the NH4
These tanks have good CO2, high light(where we often find GW in such tanks),
good everything as far the nutrients. I lowered the CO2 for a week, GW. I
shut off the filter, GW. I tossed in a ton of PO4, no GW. I tossed in a ton
of KNO3, no GW. I tossed in a ton of micro's, no GW. I did a big pruning and
removal without a water change after, GW. I added jobes, GW. New tanks by
the dozens, GW. 

It really a neat and very useful alga tool for us. It's easy to get rid of,
takes no effort and causes no real harm to the tank. But we can do all sorts
of things to it and it keeps coming back:)

FWIW, I have never had GW in any of my tanks. I had to induce it by adding
Jobes. I keep my tanks quite rich in everything but since the plants are
doing well there's little NH4+ around to be had. But I've been at work
lately checking this one out. I have some ammonium sulfate to play with to
see if it's definitely the NH4+ or not. Problem is I have to remove the
critters to do this in case I go overboard from ammonia poisoning:) But it
should not take much to trigger this event I suspect. Haven't killed things
prior with the lower amounts from Jobes, new tanks etc.
Tom Barr