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Re: N:P
>> Also, I found compelling evidence for not letting your N:P ratio fall below
>> 16:1 for aquatic plants. Neat stuff. So if you have a NO3 of 5ppm your P
>> would/should not fall below 0.3ppm or so.
>
> This number has been around for a while (25 years or so, anyway) as the
> value above which aquatic ecosystems tend to be nitrogen limited and below
> which they tend to be phosphorus limited.
I've seen it before, but went back and considered it again- knowing what I
now know and have observed.
> Be careful, though, because the
> ratio is for N and P concentrations, not NO3 and PO4 concentrations.
Oops! Oversight:) Perhaps...
But consider the the Redfield ratio which I have based this off of
(C(106)N(16)P(1) and there are other similar ratios for other sources as
well:
This balance of constituents implies the following reaction for plant
photosynthesis:
106CO2 + 122H2O + 16 HNO3 + 1 H3PO4 yeilds (106-CH20)(16-NH3)(1-H3PO4) + 138
O2's. The reverse reaction would be respiration.
The ratio is 16 to 1 N:P or N03:PO4. The weights change but not the ratios.
Did I go wrong somewhere here? If so let me know!
> A NO3:PO4 ratio of 23:1 is equivalent to an N:P ratio of 16:1, as long as
> N is available largely as NO3 and P is available largely as PO4. If
> you want nitrogen-limited conditions and have 5 ppm NO3, then you
> shouldn't let PO4 exceed about 0.2 ppm.
Steve did/does this with his pulsing of P to about 0.2ppm 2-3x a week but it
falls to zero from I recall before another addition is added. I have
experiences with much higher levels of P04 and N03.
>
> Of course you may get erratic results when you start with a value that was
> derived as an approximate rule-of-thumb for ecosystems and apply it to an
> aquarium.
Certainly, but it is interesting when figures match closely. It's
interesting to see how & why these figures may or may not match or be the
optimum.
Funny thing was, this figure was about in line with my ratio and a few other
folks.
After you have a good handle on P and algae etc and some experience (not to
mention a test kit!) they may want to try this out but I would not recommend
this for the new person:) It doesn't take much P to get up there fast! Oops!
I added a teaspoon of monobasic phosphate instead of that little old nitrate
test kit power spoon(about an 1/8 of a gram or about the size of a grain of
flourite). True story of someone I know.
An interesting idea that I am pursing is the high P with low N method. More
a 2:1 to 5:1 ratio. Maybe even a 1:1! Don't try this at home folks! Wait
till I "Toast" my tanks and get them full of algae first! I can get rid of
algae somewhat easier than most and don't mind it too much to get rid of it.
There, you have been warned!
We don't have to be so pre4cise when going after a particular ratio or level
with our tanks though. A good ballpark range is good, trying to keep it
between 15: and 16:1 would be unrealistic IMO.
Regards,
Tom Barr