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Re: Iron/Calcium/greenwater, etc.


Date: Sun, 11 Jun 2000 19:13:02 -0700
From: "Eric Johnson" <etj at nwlink_com>
Subject: Iron/Calcium/greenwater, etc

>My 55 gallon tank has a pretty bad greenwater problem right now. I've read
>everything in The Krib about greenwater, but the info there is very
>contradictory. I think there may be several causes of greenwater. Lack of
>nitrogen is certainly NOT my problem in the affected tank, in fact nitrates
>are so high I'm changing the water frequently to get them down. The
>unaffected tank has much lower nitrates><I have moved a few more
>fast-growing plants in there in an effort to out-compete the algae, but i
>haven't had time to see if that works. I think my CO2 levels are really low
>in this tank - will CO2 affect algae? In general, I've not been really
>feeding the plants in this tank for fear of feeding the algae, but that may
>be a totally wrong approach.

Let me preface my response with the declaration of my newbieness to serious
aquatic gardening.  Okay, that's the disclaimer.  But since nobody else has
jumped in (?), I'll take a whirl.  I've also been attempting to digest the
web-available info on algae etc., so I'll throw out what I've gleaned.
This is intended to provide a scaffold for other responses.  I trust that
the TRUE experts will be sure to correct my inaccuracies and will have fun
doing so!

If you haven't hit these already, I'd definitely suggest reading the Paul
Sears and Kevin Conlin algae case study reports...
http://www.thekrib.com/Plants/Fertilizer/sears-conlin.html and the article
that I believe is by Karen Randall about plant nutrition
http://aquariumfish.com/fish2/aqfm/1997/nov/aquatic/.

Okay... here goes...Algae and your plants rely on the same resources--both
have to make chlorophyll and both are in the business of photosynthesis.
Thus, when a resource is low, they end up in a competition for it.  It
seems universal that low nitrates and phosphates in the water column favors
your plants at the detriment of the algae.  Hand-waving suggests that
plants are better able to compete for these elements.   Basically you wanna
keep extra nutrients in the substrate, not in the water column.

Excess phosphate apparently favors blue-green algae (BGA/cyanobacteria).
(To see this effect, add some "pH Down" product to your tank--you, too, can
have a surreal carpet of cerulean blue!)  This is because these little
buggers are able to fix gaseous nitrogen (which constitutes 80% of our
overall atmosphere) whilst plants generally need to extract it from
nitrates.  If you have low nitrate, other algae forms become limited in
their ability to take advantage of the excess phosphate, so BGA
predominates.  (Second disclaimer: my understanding is that not all forms
of BGA are able to fix nitrogen gas, but certainly some do.)

Now...nitrate excess.  I think that this is a mixed bag, so I'm treading on
thin ice.  If there's more nitrates than your plants are able to use, any
algae would seem able to capitalize on it.  However, the paradox is (I
think) that the algae also need high phosphates--kind of a balance (?).
But if these are both high, it seems that the plants should be utilizing
them both...blah, blah, blah...

It seems that this is where light, micronutrients, and CO2 come into play
in the algae theater.  Your plants need to have all of their needs met in
order to maximally utilize nitrates and phosphates, i.e. in order to
out-compete the algae. (E.g. lack of iron can mean low chlorophyll, which
means low photosynthesis, which means reduced energy to support the
incorporation  of nitrates and phosphates into the plant.)  High light in
the presence of plenty of micro- and macronutrients BUT in the absence of
CO2 supplementation means that eventually your plant's growth will be
limited by the amount of CO2 in the water.  Any leftover nutrients could
favor the algae.  (This implies that algae can prosper in a lower CO2
concentration than plants--can someone please comment on this?  And someone
bring me back if I'm straying!!)  Presumably, providing an optimal level of
CO2 to your plants can discourage algae growth because the plants will be
able sponge up the macronutrients and thereby reduce the concentration of
these resources in the water column.  I guess the point is that CO2 doesn't
directly hurt algae, it just makes your "plant-conditioned" water column
less of a nutrient boon to them.  (Probably also means you're having to do
alot of pruning and thinning as well!)

How'd I do?

As far as feeding your plants, my scarcely educated guess (that's
disclaimer number 3) is that your plants will need the micronutrients
(iron, magnesium etc.) at sufficient (but not excessive) levels in order to
utilize the available macronutrients.  I guess fast-growing
non-substrate-feeders is a step in the right direction.  If you have
nitrate-containing fertilizer tablets in the substrate, be sure not to
disturb them during water changes.  Feed less?  Why are the nitrates high,
do you have a high fish load?  Change water like you're doing...

Now that I've thrown this out, somebody else do the right thing and clean
up after me where necessary!  THANKS!!!

-Carmen








Carmen C. Robinett, Ph.D.
Dept. of Molecular and Cell Biology
401 Barker Hall
University of California
Berkeley, CA 94720-3202
(510) 642-5971
FAX (510) 642-7846