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Re: Cyanobacteria, Algae, etc.
On Mon, 3 Jul 2000, Zach K. wrote:
> Thank you very much for your response Mr. Miller, I appreciate it. I'd
> appreciate your feedback IF you see enough of interest to get you through
> this posting, and anyone else as well.
No problem, but I suspect that when you address me (or any other
individual) that you will discourage others from answering.
> I'm attempting the phosphate limiting approach and don't know if I've
> ever achieved it.
What, specifically, are you doing to promote phosphorus limited
conditions?
> I'm wondering, under that approach, does a significant presence of cba,
> or say cba on glass in the open, above leaves, simply indicate that too much
> P is in the water column, and must be reduced, say through improving plant :
> fish ratio, assuming that all other parameters are as they should be?
I don't think the presence of cyanobacteria is diagnostic of a phosphorus
problem.
The best observation I've read on cyanobacteria came from a text called
"Environmental Microbiology", where one author observed that cyanobacteria
are ubiquitous in the environment, but only dominate under conditions that
are too extreme for other organisms to prosper. The "extreme" may be high
or low nutrients (could be just one low nutrient), high or low light, high
or low temperature, and so on.
People on this list have found several specific factors that can be
manipulated to control cyanobacteria. The one that comes most to mind is
the idea that poor circulation and low aeration may promote cyanobacteria,
and that it can be controlled by increasing circulation and aeration.
> My P levels have read very low - they look to be around .00 - .05ppm on
> my Seachem kit. (My r/o and plastic-jug Sparkletts distilled read the same,
> but it did read higher when I tried dosing P). It has a continuous range
> through those levels and beyond, but I have a hard time judging it precisely.
For clarity, are the values you're citing actually phosphorus (P)
concentrations, or are they phosphate (PO4) concentrations? Either way,
that seems low enough. I think in most tanks with phosphorus below 0.05
that something other than P is usually more limiting.
> Is P really the limiting factor in P limited tanks or is something
> else underlying it?
Perhaps I misunderstand your question, but I think that if P is the
limiting factor in a tank, the tank is P-limited by definition.
> I still don't understand the cause of their increase from fe dosing. Is
> it the fe or the chelate? Are edta or dtpa or humins a P source, or do cba
> live off of them?
If you can add something to your tank (other than P) and things grow
faster, then probably P is not the limiting factor. A functional
definition of the limiting factor is "The factor, which when changed
produces the greatest change in growth." This applies to factors other
than nutrients. I don't know what else you may be adding to your tank,
but if you add iron and see a big increase in growth then perhaps iron is
the limiting factor. In the approach that Diana Walstad describes in her
book, iron rather than phosphorus would normally be the limiting nutrient.
EDTA and DTPA don't contain phosphorus except possibly as contaminants; if
humins contain phosphorus then I think they would contain only very small
amounts of it.
The idea that cyanobacteria might feed directly off the EDTA or DTPA is
interesting. Cyanobacteria can use organic compounds as food in place of
their own photosynthetic products. I don't know if they could eat EDTA or
DTPA that way. I doubt that they could eat humins.
> I have been wondering if cba and algae could access P in leaves
> parasitically; and if low P levels could injure plants making them more
> vulnerable to attack; or if they might even lose their P, or something else
> the cba can live on, into the water even before they look like they are
> dropping leaves?
I don't know that parasitism is likely. Interestingly (to me, anyway)
aquatic plants apparently "leak" fairly large amounts of organic material
into the water. I'm not real clear on the details of that. I have read
in technical literature the speculation that leaking organics is a ploy
evolved specifically to promote growth of attached algae and
cyanobacteria. The idea is that herbivores would then concentrate on the
attached growth and leave the underlying leaf alone.
> Then I saw the 'Phosphorous and Phosphorous Control'
> postings and got to wondering if organic P was an important factor. Also,
> when looking into Hach kits I found that they have a kit which can read both
> inorganic or total P. Its twice as expensive as their inorganic-only kit.
> So I was wondering if that would be helpful or not. I'd rather not buy
> either if I don't need them because money is tight.
My sense is that you're concentrating to much on the phosphorus and that
you don't need to buy a more expensive kit. The problem lies elsewhere.
> So those were the questions behind my original posting which I hoped to
> understand better before I buy an expensive test kit, and try another super
> heavy plant load phase. Am I spinning out into la la land? If proper P
> limiting conditions exist uniformly throughout tank, does significant cba
> presence simply mean that something must be done to reduce P? And is cba's
> presence a good enough point of reference that another test kit is
> unnecessary?
Perhaps you should try a different approach. An approach that worked for
me was based on the observation I cited near the beginning of this
response, that cyanobacteria proliferates only under conditons that are
poorly suited for other organisms. To beat the cyanobacteria you need to
take a positive approach -- improve the conditions that you provide for
other plants and animals and even for algae in your tank.
I can't -- without knowing all the details of your tank -- suggest any
specific changes. You might try (for instance) increasing the light level
and setting the right light cycle, improving circulation, making sure that
your tank is getting a well-balanced set of nutrients and making sure that
your R/O water or distilled water are mixed to give a complete water
composition. Generally, think more about promoting growth in your plants
and fish then you do about suppressing the cyanobacteria.
Good luck.
Roger Miller