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Test Kits Again!

I feel a little embarrassed to tell this story, but perhaps it will help
other newbies.

I've been working with the PMDD ideas for the past 4 months with lovely
results in a 125 gal. heavily planted tank.  (Prior to that, I spent 2
years trying to learn how to "starve" a planted aquarium into good health. 
Obviously, I'm a slow learner ;-).

When I first started with PMDD, I continually got zero nitrate readings
with several of the cheap test kits.  I think I fooled around with Sera,
Tetra and Red Sea nitrate kits.  I was adding as much as 1 tsp. of KNO3 per
day and still getting zero nitrate readings.  I imagined that the K2SO4
(provided in about a 2:1 ratio to KNO3) was providing the K needed for the
plants to use the nitrates and thus, drive the nitrate levels to zero.  

Paul Sears suggested further nitrate testing to be sure the kit I was using
was working.  I bought the SeaChem nitrate test and WALLAH! it had a
reference solution (10 mg./l) and repeated tests clearly showed the
presence of nitrates in my tank.  I "read" levels in the 2-5 mg./l range. 
So I was fat, dumb and happy, as far as nitrates go.

Last week while I was in Brazil (no, I wasn't able to grab a bucket of that
beautiful laterite soil) two things happened:  My CO2 bottle ran out (I
arrived home within 35 hours of the event) and a lot of hair algae started
growing from the gravel.  In addition to the hair algae, there was more
green algae on the glass, wood and rocks than I had ever seen (since using
PMDD) and quite a bit of that green algae had a nasty, crusty look to it. 
It wasn't the soft green algae that I'm starting to get comfortable with
here and there.  A bit of cyanobacteria which had been receding was clearly
advancing again.  Other than the first signs of the beginning of crypt
meltdown, the plants looked okay, but I knew something was wrong.

So I started running tests:  Hach phosphate test (PO-19) showed just a
trace.  Iron levels (Lamotte) were low, but present.  No amonia or
nitrites.  Replacement of the CO2 bottle brought the pH back down to
6.8-7.0 and the CO2 levels up to 15 mg./l (surprisingly, the fish survived
a pH of 8.0 for a couple of days).  Then I opened my new Lamotte low range
nitrate kit and to my astonishment, obtained consistent readings in excess
of 160 mg./l!  I used distilled water and RO/DI water (in several different
tests) to dilute the sample aquarium water 1:4 and still obtained readings
off the chart!  (I took the nitrate-nitrogen readings (NO3-N) and
multiplied by 4.4 to obtain nitrate levels (NO3) which is what we care
about, right?)  This same water "read" only about 10 mg./l on the SeaChem

Following a 75% water change (with the new water testing zero for
nitrates), I'm still over 50 mg./l (again, nitrate not nitrate-nitrogen,
right?)!  I'll keep doing daily water changes until the nitrate is under

I don't know how much of this problem might be attributable to 35 hours
without CO2, but I have the feeling I've been running at absurd levels of
nitrate for a month or two.  Does anyone think the nitrate levels could
have spiked in just over the two days without CO2?  Maybe the astonishing
point is that a fairly (otherwise) well-run PMDD set up was able to sustain
up to 200 mg./l nitrate without self destructing!  If I've got this story
right, I just don't know how a beginner could judge nitrate levels using
the cheap kits???

Now for some good news:

A friend of mine got his Ph.D. in the metabolism of P and K in grapevines. 
He loaned me a "Horiba compact ion meter" which he uses to measure the K
ion levels in grapvines (the leaves and soft stem tissue is squeezed
through a garlic press to make the sample liquid).  This little gadget is
about the size of two credit cards and costs about $400.  It's available
from Spectrum Technologies, Inc. Plainfield, IL (800-248-8873).  The
instructions state that it works on the "ion electrode" method (whatever
that is).  You put 2-5 drops of sample liquid on a half inch plate with two
"sensors."  In the 1-100 ppm range, it claims an accuracy of 1 ppm.

I know a lot of us are interested in K levels in our PMDD tanks and how to
"tweak" the PMDD for K.  For the good of the order, I would be willing to
put this little gadget to use in any experiments that you smart guys out
there think would be helpful.  Any ideas?

Regards, Steve Dixon