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Red Algae and Nutrients

Well, I promised Dave Whittaker that I would post my tank
parameters after checking them this weekend.  This pertains to our
discussion on red algae, but I think it'll get too confusing if I repost
the entire thread.  Anyway, here goes:

Now, I try to do a weekly water change and I only fertilize at water
changes, however I missed last week's, so the following parameters
are for a 20 gallon long that has 2-week-old water in it:

pH and CO2 concentration will vary considerably depending on the
viability of  the yeast in my DIY generator.  It can range from about
6.4 up to about 7.2 in the early morning (my tap water is about 7.4).

dGH of my tap water is 7.5 degrees (about 133 mg/L) but I dilute it
down to about 7 degrees (125 mg/L) with a little DI water at water

dKH of tap water is 5 degrees (90 mg/L alkalinity); (dilutes down to 4
degrees or 70 mg/L  alkalinity with DI).

Nitrate Nitrogen measured with a LaMotte kit, was hovering around
1 ppm (X 4.4 = about 4 or 5 mg/L NO3).  I was surprised to find it
this low.  Coincidentally, this is what my tap water measured out at,
so it appears that I've achieved some sort of equilibrium.

Phosphate was hard to determine, even with a LaMotte.  I guess my
eyes aren't what they used to be, so I'll just call it "trace".  Since I
have no algae at all, I assume there can't be much phosphate at all
in the water column.

Iron was the big surprise.  Almost undetectable, although I see no
signs of iron defficiency in my plants.  The duckweed, which is
supposed to be an iron indicator plant  is green and multiplying like
crazy, so I'd be reluctant to boost my dosage.  I am currently only
adding 1.5 mLs. of Kent's trace elements with iron, along with 3 mLs
of Duplagan at water changes.  I am not using any fertilizer tablets
at all, but do have a laterite/gravel substrate.  I remeasured just a
couple of hours after the water change and found virtually no
difference in the iron level.  I even suspected a defective kit until I
checked it out with a solution that I made up.  I suppose the plants
must be stocking the iron as soon as it becomes available and
utilizing it during the course of the week or two that there is between
water changes.  Still, this makes me wonder if our target level of 0.1
mg/L isn't still too high.  Perhaps we are giving the wrong impression
that it should be *sustained* at that level.  I will continue to monitor
my iron levels without changing my current fertilizer regime.  I will
also look for signs of iron defficiency.

Anyway, I don't have Siamese algae eaters (real or false) and I have
an aquarium that doesn't have a trace of red algae in it. In fact, it
doesn't appear to have any algae in it.  It wasn't always that way, but
I managed to hit on the correct balance of nutrients.  There is no
substitute for water changes and moderation when it comes to
adding fertilizer.  Of course, having decent tap water helps a lot.
Perhaps our motto should be:

 "Be generous with your water and frugal with your fertilizer."



P.S. The other two otos showed up this weekend, so they are all well
and accounted for.
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