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Karsten wrote in #767:

> So I was getting a little curious because I've read
> so much about the influence of Nitrates to the growth
> of Algae. My Nitrate levels were around 5-10 ppm before
> I started the test. Then I raised them (fertilizer
> tablets) to about 50ppm (!) and kept this level for
> 4 weeks. And guess what: nothing changed in the tank.
> No Algae were growing, the plants totally behaved like
> before.

I conducted a similar test (although I wasn't aware of it 
at the time!).  Not until my nitrate levels reached
140 ppm or so did I notice strange things in my tank.  It 
wasn't even that bad--mostly just some darker forms of 
algae starting to cover the leaves and some hair algae.  
The plants weren't growing as well or uniformly, but they 
weren't dying off either.  Paul Sears mentioned a few months 
ago that a high nitrate level by itself is not much 
of a problem in planted aquariums; and the large Dupla 
aquarium is reported in TOA to run at about 30 ppm nitrate.  
So what you report doesn't surprise me at all.

> Also, I raised the Fe level to .5ppm for about 3 weeks
> with no visible change in plant or algae growth. What
> actually is supposed to happen with a too high Fe level?
> .5 ppm did not do anything to my tank. But anyway, when I
> stopped fertilizing with Fe (levels dropped to not detectable),
> the plants stopped growing and a few were even looking 
> very sad, so I started adding Fe again.

This surprises me greatly!  If I were ever to raise the Fe 
levels in my tank to anything approaching .5 ppm, I would have
a hair algae problem in 2 or 3 days and a darker algae would 
slowly start to cover the leaves of many of my plants within a 
week or so.  In fact if I even approach .1 ppm Fe, I get an 
algae outbreak.  

I sit here in San Francisco and regard this .1 ppm Fe PMDD claim 
that everyone seems to make as not reproducible (at least by me).  
Using Hach and LaMotte iron test kits, I find over and over again 
that I need to keep iron at just over a trace say, in the 
.2 - .3 ppm range, or else I'm in algae trouble.  I really wish 
we could get to the bottom of this issue.  

What kind of iron are you adding and what test kits do you use to 
measure iron?

Regards, Steve Dixon