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Potassium and CF Lighting
While I'm at it let me offer up an observation I've been meaning to post for
a while, and ask a question about CF lighting.
Potassium. I bought the LaMotte potassium test kit a couple of months ago
and have tested my tanks fairly frequently and tested the kit against
various reference solutions (from Hach). Let me say first that I'm
surprisingly pleased with the kit. While it is a little odd trying to look
down a tube at a black dot through a haze of white precipitate, the kit is
fairly readable actually, and gives good readings in the range of 5 - 50
ppm, which is what we're interested in. My Hach reference solution was 100
ppm so it was very easy to make up different test solutions by diluting the
reference with distilled water. I would say I have confidence in the kit
picking out increments of say, 5 ppm K. For $36 its seems to me a fairly
inexpensive way to get some baseline info on this important macronutrient.
Now for the info. Both of my tanks tested in the 25 - 35 ppm K range
consistently. I supplement KNO3 to keep just above detectable levels of
nitrate (about ½ tsp. per week in my 125 gal. tank and about 1/4th tsp. per
week in my 40 gallon tank) and on occasion I have added 1/4th tsp. of K2SO4
because I never really had any idea of what my potassium levels were and I
thought perhaps some more might help.
It may take another month or two to be sure of this conclusion, but it seems
under my conditions (high light, quite a bit of CO2, supplemental micro and
macro nutrients, and good growth) that KNO3 added to keep detectable NO3
levels will by itself result in K levels in excess of 10 ppm and perhaps as
high as 20 ppm. I've dropped all supplementation with K2SO4 in order to
determine what KNO3 will do by itself under my conditions.
It is also reasonably clear to me that I have routinely run for a couple of
years now in the 25 - 35 ppm K range and perhaps even somewhat above that
level (through unknowledgeable K2SO4 supplementation). So my tentative
conclusion is that potassium, as we have found with nitrate, is not so
problematic at higher levels. And in addition, that both potassium and
nitrate together in excess do not seem to present any unusual problems. A
number of you have seen my tanks and I think I can say with confidence they
are not overrun with algae or other gross problems. Plant growth is good
and algae is within the usual spot algae on the glass/a few older leaves
When we were first discussing K a couple of years ago, dr. dave (Heubert),
our resident Ph.D. aquatic botanist, (are you still out there dr. dave?)
suggested that we should target K levels in the 5 - 10 ppm range. A
personal friend of mine, a Ph.D. viticulturalist with an undergraduate
degree in aquatic biology, offered just a guess that 100 ppm might be a
desirable range. I have always aimed for the lower level. Having said
that, I have also always been of the view that some extra potassium has
given my plants a very nice boost and vibrant growth, definitely one of the
keys for improving my skill in the hobby.
What is our current thinking on K? Does the information I'm reporting
square or conflict with your views and observations? Thanks.
Compact Fluorescent Lighting. I'm perplexed by various claims regarding the
light output of CF lighting. Many of us (myself included) have reported
good results with these lights. The bulbs between 5000K and 6700K seem to
work very well for planted aquariums. We all notice/report how bright the
lights seem and how our plants are pearling more and growing well.
There are a number of reports, starting with the manufacturers
(CustomSeaLife, for example), that CF light produce more light per watt than
regular (NO) fluorescent bulbs, including more light than the new efficient
T-8 bulbs. Now I realize the term "lumen" includes an element of human
perception. That a light might seem "bright" to the eye and yet a bulb that
seems less bright might actually have more output as measured in lumens,
that perception of light may not correlate with the actual output of the
bulb-referred to as PAR, if I recall.
Am I right in recalling that PAR ratings would give us a rating which would
better correlate with plants general ability to use light than lumens?
A few weeks ago Michael Rubin sent me a copy of a note from Erik Olson
which, if I paraphrase correctly, essentially stated that CF lights are not
in fact more efficient, that they do not put out more light per watt than
normal fluorescent bulbs. I do not recall if Erik was referring to lumen or
PAR output. One of Erik's points was that the technology of the two types
of bulbs was more or less the same--however it is that these bulbs actually
Just to make a stupid observation of my own, all seem to agree that the new
T-8 bulbs are more efficient, which I take to mean that T-8 bulbs put out
more light per watt (again, I'm not sure if we mean lumens or PAR when this
is said) than the old T-12 bulbs. So perhaps simply saying that all of
these bulbs use the same technology doesn't really answer the efficiency
Does anyone have a definitive answer to this question? Do CF bulbs put out
more light per watt (lumen or PAR) than regular fluorescent bulbs; than T-8
bulbs? Do we have data on this point?
Thanks for you views, and apologies for my use of the bandwidth today.
Regards, Steve Dixon San Francisco