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I've CC'd the APD since your question is of general interest.
Michael Rubin wrote:
> Hi Steve,
> I've read your posts to APD with interest over the past several months (I'm
> a newbie, but an informed one), and today you surprised me. I wonder if
> you'd be willing to give me a little advice?
> > here are some [PMDD] targets:
> > N as NO3 2-5 ppm (or use substrate N)
> > K as K 2-50 ppm
> > Ca as Ca 5-50 ppm
> > Mg as Mg 3-30 ppm (keep it lower than the Ca)
> > S as S 2-50 ppm
> > Fe as Fe 0.01-0.1 ppm (or use substrate Fe)
> > P as P 0.1 - 0.5 ppm (or use substrate P)
> First a little background. I set up a 50g community fish tank last
> December, only to find I liked planted tanks, so I rebuilt it 3-4 months ago
> with a Flourite substrate, 110w PC lighting and injected CO2. I went
> thorugh the normal agonies most newbies do (at one point I counted 6
> different kinds of algae), but I seem to have hit the sweet spot as of about
> a month ago. No visible algae and everything is growing like crazy.
> My dosing routine is simple, based on the high quality of my local water
> (3.0dGH, 3.0dKH, 0.2 ppm PO4):
> * change 15-20 gallons each week
> * test for nitrate/nitrites and PO4 3x weekly, adding 1/4 tsp of
> either K2SO4 or KNO3 depending on test results (I usually see trace
> nitrate/nitrite and about 0.1ppm PO4)
> * test for Fe, adding 5ml Seachem Flourish Iron 3x weekly depending on
> results (it's GONE in 2 days)
> * TMG 5ml 3x weekly
> * nylon bag of dolomite maintains 4.0dGH and 4.0dKH
> * 24-30 ppm CO2 give or take
> Two weeks ago I added 8 Jobes sticks (16-2-6). I didn't realize that was a
> lot until Tom Barr warned me to be ready to change 50% of my water every
> day. So far the only differenc I've noticed in the water column is that the
> tank doesn't burn nitrate as fast. I switched to K2SO4 for awhile, but
> switched back to KNO3 recently.
> I've been VERY careful with the KNO3. I've been avoiding adding it uless I
> see at least some trace of PO4, and when I test the tank a day after adding
> it I see less than 0.02 ppm (using the Seachem Multitest Nitrite/Nitrate
> test kit, in which I don't have a great deal of faith - I'll be beta-testing
> their new test kit as soon as Greg Morin sends it). So you can see how
> surprised I was to read your target of 2-5ppm. I would need to add a LOT of
> KNO3 to 50 gallons to raise nitrate levels that high, but I'm seeing signs
> that might be attributable to N limitation: my Anubias nana has yelowish
> new growth, and my jungle vals leaves, which are growing to the surface in
> just a few days, develop rot over their entire length shortly after they've
> grown out. I drow Salvinia, a known nitate and potassium sink, and I'm
> constantly forced to throw away handfuls. E. bleheri, E. tenellus
> micro-sags, corkscrew vals are all doing very well. R. macranda has nice
> color and is developing into a forest. No algae to speak of except some
> green spot on the glass, which I buff off once a week.
> I guess I'm asking if I'm missing something. I have the impression that
> raising NO3 levels increases the risk of algae bloom, but I'm not sure where
> the threshold is. Any advice?
The 2-5 ppm of nitrate is possibly the most controversial target. If you
had significant phosphates in a tank that was nitrate limited, certainly
adding a dose of nitrate is probably going to induce an algae bloom
depending upon the plant biomass, the type of plants (fast growing,
opportunistic) and how much existing algae is in the tank. The original
question by Richard Sexton was in the context of mixing his own PMDD
brew and using that regime, you dose nitrogen until there is a surplus.
This will drive the phosphate concentration down (by assimilation into
the biomass of the growing plants) until phosphate is the limiting
growth factor. It is critical that other growth factors such as light,
CO2 and all the other nutrients are sufficient (surplus). If CO2 or any
other factor is in shortage, a large dose of nitrate, in my experience,
seems to cause a bloom of cyanobacteria (blue-green "algae"). If there
is plenty of phosphate, you can also end up with a green water bloom.
Your strategy of only adding nitrate when phosphates start to show up is
a viable strategy however you might find it easier to measure nitrate
concentration and dose when it drops too low. That way, your plants will
never be nitrogen limited. In good lighting, plants which are nitrogen
limited will be yellowish and growth rates will not be high.
When growth is limited by phosphate, if you dose with a high dose of
nitrate, in my experience, you tend to get cyanobacteria but that should
not be a risk at 5ppm or less of nitrate.
Steve Pushak Vancouver, BC, CANADA
Visit "Steve's Aquatic Page" http://home.infinet.net/teban/
for LOTS of pics, tips and links for aquatic gardening!!!