Re: Phosphates

On Wednesday, 13 March 1996, Dionigi Maladorno wrote:

> 1) I have a VHO ballast, and the light output is supposed to be 95W for each
> 3' tube. This gives a ratio of  2.1 Watt/gallon, with a total output of 380
> W.

OK, I think you have enough light.  Remember though that VHO lamps are
less efficient than normal lamps.

> The floating plants however screen some light away, and the yellow/brown
> pigments and particles coming from peat certainly absorbed a lot of it.
> Without peat I see the water being much more clear, with more efficient
> light transmission.

True.  Thin the floating plants regularly and use less peat (unless of course
you want the nice blackwater look).

> 2) Please send me some clarifications on the use of K2SO4 (is this potash? I
> could not understand well the issue from the recent postings) and KNO4. The
> floating plants are growing like crazy, as well as some of the submersed
> plats (albeit a minority). Wouldn't trace- and macro-element deficiency be
> incompatible with this? My discus and I also do not want (if possible) to
> raise hardness and pH.

K2SO4 is potassium sulfate, KNO3 is potassium nitrate.  Neither they nor
the trace elements will affect your pH or hardness (to a first approximation).
Mg will harden your water but you don't need much.  Everything you add
that doesn't get consumed by the plants will increase your total dissolved
solids.  I doubt that this will be a problem.

At the moment you are probably nitrate limited as shown by the good growth
of cyanobacteria.  KNO3 alone will probably help, but once you add it
there is the possibility that the plant growth will be limited by something
other than phosphate.  This is why Paul and I recommend adding trace elements
whether you think you need them or not.  Try adding a 1/4tsp KNO3 a day to get
your nitrates into the 10ppm range and see if this helps.  If in a few weeks
the cyanobacteria are replaced by green algae, you will probably need
K2SO4 and/or trace elements.  Once you've tweaked the nutrient levels in
your tank you should see very little algae of any kind.

> However, since the tables might
> indeed somewhat contribute to the problem, I will make a little experiment
> dissolving a table in a bucket and testing the water. I will let you know
> how it goes.

I'm sure you'll find the tablets full of phosphate.  The peat may have been
storing it for you, but I doubt that it's a natural source of phosphate.
Your tap water seems to have very high phosphate levels; I hope you don't
drink the stuff.

> Isn't this fun??

Absolutely!  I love playing with other people's tanks!

> P.S. If you have the chance in your paper to review the interactions between
> PO4 and iron, this would be very interesting. Could this prevent plants from
> using it? Maybe all the iron in my tank is useless for plants? 

We aren't planning to address the issue.  I would guess that if a
test kit shows a measurable amount of iron, the plants will have
access to that iron, but I'm out of my league here.  I don't really know
what an iron test kit measures (Fe++, Fe+3, or something else entirely).
Kevin Conlin   kcconlin at cae_ca   "We're Canadians.  We HAVE to be polite"
Finger as332 at freenet_carleton.ca for PGP public key.