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Phospate in the Water Column
Karen wrote: " I have found that with .5 ppm phosphate in the tap water
that not only do I not have algae problems, but in high light, fast growth
tanks, the plants perk right up with a water change... a phenomenon I
attribute to the influx of PO4. Even when I set up a new tank, I haven't
had algae problems, and that initial .5 reading quickly drops to
undetectable in the tanks.
So I guess, heresy or not, I agree with you ;-)" Love that frown, Karen!
:-)
Tom Barr and I were discussing this point as well this morning. I've been a
little casual in the past few weeks (working way too many hours and adding
pinches of this and that to my tanks without paying a lot of attention)-so I
decided to break out all of my test kits this morning (all Hach and
LaMotte). In both of my tanks I measured Nitrate at about 20 ppm (higher
than I aim for, but I know from experience no problem at all); 30 ppm
potassium (no problem with this level under a variety of conditions for 2
years now); 0.07 ppm iron (okay, but I'm touchy on iron, and would like to
see it at 0.05 ppm or less; and 0.5 ppm phosphate (much higher than I would
ever aim for).
Now I've intentionally been adding some extra macronutrients to my tanks for
the past couple of months to see the effects on 'allegedly' slower growing
plants (such as crypts and anubias) and my strategy has been to be sure that
sufficient micronutrients were available. I'm also very interested in how
long it takes "topped" stem plants to pick up under good conditions (not
long). I use TMG (Tropica Master Grow) and Flourish (just topping off the
TMG) and if I perceive that I'm light on iron, (TMG is light on iron IMHO
for soft water high growth conditions) a touch of Flourish Iron for
micronutrient supplementation. My dosing of micronutrients is entirely
observational: if there isn't reasonably good pearling in the tank I
consider adding a few ml of one or another micronutrient solution.
During this period of time when I had relatively high levels of
macronutrients, I have had no algae problems whatsoever. (That is not to
say, that slight amounts of green algae are not present on the glass (they
are), but interestingly, even this little bit of 'regular' algae has been
slightly less than usual.) So my preliminary conclusion is that 'moderate'
(uh-oh in trouble again, Roger) levels of macronutrients are NOT problematic
if sufficient micronutrients are present to support good plant metabolism.
Perhaps the problem with 'excess' but moderate macronutrients is the
creation of a micronutrient-limited situation, leading to algae growth.
I always worry that everything I say (and even think) is limited to soft
water conditions, but if Karen is reporting something similar in hard water
conditions, perhaps we're on to something.
Let me confirm that R. macranda thrives under this condition and add another
species: Eusteralis stellata has benefited even more that the macranda from
the extra PO4. And finally from the 50,000 feet level, this observation
would appear to be consistent with high macronutrient levels reported in the
water mains in Europe (how's that for sloppy anecdotal non-science!).
Regards, Steve Dixon in San Francisco where we had a sunny day today!