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Re: Iron levels
With regards to the different nutrient levels that have been suggested here,
I went back and re-read the Sears Conlin paper and all of the associated
follow-ups as archived on the KRIB. One thing I noticed right off the bat
was that it was based upon two case studies, a 500L tank with 240W of
illumination and a 160L tank with 80W of illumination. By my math, the
lighting levels work out to 1.8 Watts/Gal. and 1.9 Watts/Gal.
Test case #1 was originally set up without any additional CO2 injection and
only later was a yeast generator introduced, eventually upgraded to
compressed gas. CO2 levels were apparently not monitored (although pH was
noted). Test case #2 had CO2 injected from the start but again, no record
seems to have been kept of the CO2 levels. But in the recommendations
section of the paper, a specific range of CO2 level is given (10-15 ppm
CO2). Some of the recommendations appear to be based, at least in part, on
earlier work done by Dupla (i.e Iron levels and quite possibly the CO2
levels)
The research was also carried out in 1993 and 1994. What might have been
considered "high lighting" then is hardly what we commonly see bantered
around here today - in some circles, anything less than 3 Watts/Gal. are
sneered at.
An aquarium is in many ways like an engine, it can run at varying speeds
depending upon how it is throttled. More gas, more air, more rpm and more
power.
It is _quite_ possible that the "accepted" levels of nutrient dosing, which
were based upon tanks run at "slower speeds", are inappropriate under
conditions of _really_ high light and very enriched CO2 levels.
I'm certainly not knocking the work done by Sears-Conlin, nor their
conclusions. Their paper and the subsequent follow up work contributed to
their thesis by many others has enabled loads of people to grow beautiful
aquatic gardens. Nor am I criticizing Tom and his "richer mixtures" (my
quotation marks). Within the parameters that each type of tank are set up
and maintained (low-moderate light, moderate or low levels of additional CO2
introduced vs. high to extreme light levels and very rich CO2 additions) it
is only understandable that the plants might be able to take advantage of
vastly different nutrient levels.
However as I noted earlier, a tank run at a moderate speed is probably going
to be easier to stabilize in a "steady state" than one which is running
faster - i.e. more maintenance and monitoring is going to be needed in the
high light, high nutrient case.
You also have to consider the plant mix and mass involved. Some plants grow
much faster than others and can probably benefit from the extra nutrients -
do you _want_ to be pruning your plants every week and can the plants you
are growing handle all of those extra nutrients?
As Erik Leung noted, the "look" of a well running high input tank is
absolutely awesome - it really can "sparkle". However, this isn't a cake
mix....you can't take 2 cups of this and add 3 tsp. of that, mix and bake
for 15 minutes at 350F and be assured of "Betty Crocker" goodness every
time. Nutrient levels (and additions) are going to vary for each and every
tank and also over time within each tank - you can't use someone else's
levels as your own because their tank is probably different from your tank.
Each of us has to find the "sweet spot" for our own tanks by careful
observation. The "trend" to higher nutrient levels for high light tanks
might be correct but it would probably be wise to "ramp up" the additions
slowly and over a period of time (just as it might be wise to ramp up the
light levels and/or duration over a period of time).
James Purchase
Toronto