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Tom Barr wrote:
>Hoagland's solution....Elemental ratio's - 3.6: 1 : 3.8
>Looking at the solution and the compounds that make up the solution I see
>that KNO3 is the main source of N but the ratio of NH4 to NO4 is about 1.75
>NO3 to 1 NH4. (Source: Epstein 1972)
>KNO3: 1M 6.0mls N 224ppm
>Ca(NO3)2*4H2O 1M 4.0mls K 235ppm
>NH4H2PO4 1M 2.0mls Ca 160ppm
Looks like the CaNO3 also helps to supply NO3 to make final N:K into 1:1
>I suppose the ratio would work well at 5:1:30. Or 10:1:40 etc. Depends on
So for now, lets agree that P needs to be relatively later. I will come
back to N:K below.
>Hoagland levels are set at the highest possible
>concentrations without producing toxicity symptoms or salinity stress. Many
>researchers dilute the solution and replenish it frequently in order to
>minimize fluctuations of nutrient concentrations and in the plant tissues.
Let's assume that most people will use lower concentrations in their tanks.
>I could limit growth..... What is defined as minimal? When your
>plant dies? Stops growing? Gets holes from a deficiency? Gets covered in
Let's keep "stop growing"... and add: grows slowly, and looks nice.
> Different parts of the plant also have different ratios, if
>you use all leaves you could get very high MN:Mg ratios but not in the
Lets think in terms of old leaves and new leaves... and look at roots
separately, to see if plant behavior may be different.
>Just going on observations 10:1:50 is nice but not the minimum.
Is this what you add, or what you want in the water. Ideally, we should be
checking to see what is in the tissue, but use inputs as a proxy.
>2ppm of NO3 is my personal cut off point for that species of N. K? about
>2-3ppm but some species, fast growers in particular are more sensitive to
>variations and lower tolerances IME.
>A crypt can/could handle less than 2ppm of NO3(they uptake NH4 namely) and
>slow growing vs something like Riccia (fast growing and loves K and NO3)
>would react differently.
This is complicated, but because we are using dilute solutions, I think we
need to look at LEVEL and RATIO. Combinations of the two may also be
>PO4? I think less than .2ppm certainly but is the .2ppm inorganic P04? You
>can run it down to 0.00ppm for a day or two with no ill effects on all 3 but
>you'll need to add more after that. Depends on the time frame your talking
Dont forget substrate phosphate which are rarely included in the equation.
....however, I have recently learned that water column phosphates is more
important for some species.
>> In that
>> regard, is KNO3 a good source of N and K, because it provides N and K in
>> the ratio 14:39 (~1:3). I dont like to overdose K in soft water.
>?? What do you consider overdosing? Interference with Ca uptake? Folks in
>the bay area have soft water and I deal with tanks there and they have no
>problems with 30ppm or so. Certainly nothing that would appear as a Ca issue
>that I can tell. I don't go over 50ppm but a 40ppm has been added and Im
>sure abuses go on but we hear little horror stories of K
>overdosing...........and that's a good thing:)
Yes, I was thinking about interference with Ca uptake. There is soft water
and very soft water. If you or other people in bay area are carefully
adding/replenishing their Ca and, lets say, keeping 4<GH<6, then 50ppm K
wont be a problem. But if (1)Ca addition is not part of your normal routine
and you have very soft water (my tap water has 10ppm Ca and if I dont keep
up, it definitely goes down from there) and (2) you are regularly adding
KNO3, then the K:Ca ratio can get out of whack. I noticed that among my 3
largest higher light/faster growing tanks, that one was doing poorly. This
was one that got the most additions of inorganic macros. After finally
testing for K, I found it had 50ppm K whereas the good tanks had 20-30ppm.
After doing major water changes, the poor tank improved.... but it took
months for the plants to show it. Of course, water changes correct MANY
problems, but this is one piece of anecdotal evidence that made me concerned.
BTW, in natural waters, there is 5-10x more Ca than K
But, when I check critical conc ratios and nutrient solutions like
Hoaglands, there is 2-3 more K than Ca. So...????....... maybe high K is
only an issue when K:Ca ratio is really out of whack?
>As a matter of fact I've never heard one, have you?
>I've seen some KCL issues but it was the CL, not the K.
Maybe in my case it was the Cl-, but in other long established tanks (over
10 years), where I only use KCl and not KNO3... I did not see long term
problems. Also, if my K is coming from KCl, then 50ppm K means the same Cl
concentration. That corresponds to adding 1/4 tsp per gallon. Is this a
lot of cloride? Dont people routinely add NaCl to fish tanks for
prophyllatic purposes (yes, they may not have plants). I found a formula
in an old aquarium book to replenish distilled water which says to add
1/3t of table salt per gallon!! This would mean even higher Cl. I once had
Cl- tested in my tanks, and they were 20-30ppm. Although this is much more
than natural waters (typically <10ppm), it does not appear to be so much.
One of my references on hydropics says that a nutrient solution containing
about 10-20ppm of Cl is required for optimal growth. With excess (in
terrestrial plants) it says you get small dull green leaves.
>> do we want to provide the certain ratios to get the best plant
>>growth, to produce a certain morphology (color, size, shape),
>Well the red color thing we started on a few years ago surely shows some
>Higher NO3 more green and faster growth in many(most) species.
>Lower NO3 redder colors.
>PO4 stress also can produce redder colors.
>Higher P to lower N ratio helps also in many species.
My red plant tanks have very low P (at least in the water) and low NO3 but
>But algae has the ***same opportunity*** to get the PO4(or NH4 or NO3 etc)
>as the plant if it's in the water column. If there's some there, the algae
>can use it. But this doesn't happen _unless_ the plant is doing poorly. I
>think something else is going on. It's not resource competition. Both have
>had that pressure removed by adding excess of that nutrient and other
Can it be allelochemicals which HEALTHY plants produce? Same for specific
species of luxuriant algae. Once something is dominant is stays dominant
for a while. Under those conditions, you can be liberal with nutrients. The
novice may not know what healthy plants look like until they see it for the
first time in someone elses tank.
>> and this leaves excess food
>> which may contribute to more algae.
>The plant leaks "food"(nutrients) and then this is also food for the plants
>and the algae.
>This line of thought doesn't address the underlying issue of availability to
>the plants and the algae. Algae still have the same access as the plants do
>to this "food". Why don't the plants re-sorb this "food"?
I was wondering if they can only store so much and then they are more prone
>I like the ideas, but the practical side? Will knowing that in a certain
>narrow range of parameters that a plant species will leak PO4 laden residue
>into the water column where it may (or may not) be used by algae instead of
>the plants help us in the end? I'm skeptical about that issue.
Not if allelochemicals (or something similar?) is going on. But if the
algae can re-establish when extra chemicals become available, then maybe.
Shouldnt we allow for the possiblity that the plants will start to do
poorly for some random reason and then the waiting algae will take
advantage of the situation. If plants are storing nutrients up to their
capacity, then when one species declines, the others may not be able to
sponge it all up... and then the water column concentrations increase.... I
suppose regular water changes together with an experience eye will help.
Neil Frank / Aquarian Subjects
Interesting old books and magazines (but most plant books are already gone)