# Re: NPK

• To: <Aquatic-Plants at actwin_com>
• Subject: Re: NPK
• From: Thomas Barr <tcbiii at earthlink_net>
• Date: Sun, 13 Jan 2002 22:32:45 -0800
• User-Agent: Microsoft-Outlook-Express-Macintosh-Edition/5.02.2022

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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)

Elemental

>> KNO3:         1M 6.0mls            N  224ppm

N= 84mg/l or ppm

>> Ca(NO3)2*4H2O 1M 4.0mls            K  235ppm

N= 56 x 2 =
>> NH4H2PO4      1M 2.0mls            Ca 160ppm

N= 28ppm

> Looks like the CaNO3 also helps to supply NO3 to make final N:K into 1:1

I was correct.

This _was_ included in their elemental ratios. This is based on the total
elemental of all the additives not just one salt for one Nutrient source.
Just look at N from NO3 then. A 1 M solution of N from KNO3 would give 14
grams/mole in a liter of N or 14000 mg of N in a liter. 14000ppm(or mg/l) x
.006liters(in 6mls)  = 84ppm for KNO3 alone. Adding the other 3 sources of N
up you'll find it hits 224ppm. So the ratio first stated was correct.

3.6 :1: 3.8

This ratio in this solution also addresses the NH4 to NO3 ratio of 1:7. I've
read figures shooting for a 1:4 ratio but this would be better for our
purposes if it was a wider range.

28ppm NH4 : 196ppm NO3 close to 1:7.

>> 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.

Hope so:) Probably explosive:)
>
>> I could limit growth.....  What is defined as minimal? When your
>> plant dies? Stops growing? Gets holes from a deficiency? Gets covered in
>> algae?
>
> Let's keep "stop growing"... and add: grows slowly, and looks nice.

So stops growing mass wise? No new tissue?

>> 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
>> roots.
>
> Lets think in terms of old leaves and new leaves... and look at roots
> separately, to see if plant behavior may be different.

Ummm, I think if you look at leaf nutrient ratios they are quite different
from ratios elsewhere in the plant(Mn:Mg is just one, iron leaves are quite
higher in the leaf as are a few others). Most ratios of nutrients are for
Whole plant, not separate.
If you do a dry analysis you'll quickly see this.

One way around this would be to use non rooted plants(Riccia seems like a
good one for this). But would it be as realistic? Hygro would be a good one.

>> 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.

Assuming the concentration is equal to internal concentration is a fair
assumption. Some uptake can used by bacteria and algae (a small amount
relative to the plants). Some can be from complexes, binding and
precipitation. At some point, the sites for binding (say laterite) are
exhausted. They simply fill up and no longer accept PO4. Older established
tanks certain experience this. The only place left for the PO4 is in the
plant tissue.

Using a bare tank and Riccia can show this also.

>> 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.

I think adding that may be  difficult for us to trace. Floating plants are
good since we can at least get a good idea that they have enough light,CO2
and they take only water column nutrients. That simplifies that issue.

> 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.

Okay, now consider this:
Is it simple Ca limitation rather than high K causing this problem? Ca
uptake is a _slower_ process. High concentrations will help drive Ca into
plant tissue. That would speed it up. Also having high plant growth at low
levels of Ca may simply exceed the uptake.

K and Ca are antagonistic in a number of biochemical pathways but it's
interesting to see/hear about the possible effects of Ca
limitations/blockage (say 20-30ppm vs 50ppm). But it seems it could be a
simple Ca limitation also. If you get down in those ranges a few things can
happen. What was the source of K? KCL or K2SO4?

This K idea is neat but folks don't keep GH's or Ca this low normally. I
certainly would not recommend Ca @ 10ppm. Too risky. Higher levels don't
bother plants anyway.
>
> BTW, in natural waters, there is 5-10x more Ca than K

Which waters? Or tap waters? Natural waters have huge ranges. If you look at
the Dupla book it shows ranges in the 1:1 to 1:3 ranges or so for natural
waters they address. In karst limestone regions I'm sure it's very high Ca
range(say KY and TN).

> 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?

That would be my experience. GH should be 3 or higher. I find it interesting
to see odd tap waters. Roger Miller's tap has weird make up(like it's
salt(NaCL) softened).
Yours is pretty darn soft.

> 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?

I have had a few folks complain about higher levels(above 20-30ppm of K)
using KCL. They switched to K2SO4 and the problem went away. I do not use
KCL. I think CL is going to be more trouble than SO4 when you push it up in
concentration.

> 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.

Most of those Hydroponic mixes are very concentrated compared to what we
back on N and P and K:)
Maybe I'll get to CL later:-) I'll keep the K2SO4 thank you. I know what
high levels of SO4 do (nothing). CL? Not sure.

> My red plant tanks have very low P (at least in the water) and low NO3 but
> high N:P.

So a 5:1 ratio? See Rubin's comments. I think SFBAAPS should get those old
archives out and we should present some finding on this issue for the APD.

>> 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
>> essentials.
>
> Can it be allelochemicals which HEALTHY plants produce?

No, large water changes remove this issue. I've done 70% every other day.
Carbon should also remove large organic substances and that could be used
also.

There is the possibility that the alleochemicals are extremely effective at
low and high levels(say you only need 10^-12M to work well). But if that
were the case? You'd only need a few plants in a tank or fresh tank water
from a tank doing well to remove algae etc. We don't find that to be the
case. It would be great snake oil in a bottle if you could bottle it:)
"Tom and Neil's Magic Allelochemical Water Tonic":)

I can see this in a non CO2 no water change tank happening. I'm a little
skeptical we experience this. Most of the observations I have show DO
related issues.
I think it has much more to do with photorespiration process differences
between the plants and algae when CO2 is used or is used up.

> Same for specific
> species of luxuriant algae.

GW might do this. Again water changes and addition of nutrient back in will
show this not to be the case unless at very low level interaction between
competing species. You can easily do water changes daily and still not get
rid of GW. You can also add back the nutrients each time that you have
removed. I've done this and still got a similar result. Most algae cannot
deal with this treatment.
It would be nice to extract this chemical inhibitor(if it exist and will not
cause plant harm) and use it for our tanks. It(GW) does not seem to effect
the plants and a few other species of algae except by lowering the lighting.
The light effect may be the only real effect going on.

> Once something is dominant is stays dominant
> for a while.

King of the mountain idea. Adults have a higher survivorship and much lower
maintenance needs.

> Under those conditions, you can be liberal with nutrients.

I agree you can but is it due to plant removal of the nutrients? The algae
still have the access whether the plant is there or not or in mass. We still
add the same concentrations of nutrients. The algae still have good access
to recruitment space, light, nutrients etc. These are not in short supply.

The
> novice may not know what healthy plants look like until they see it for the
> first time in someone elses tank.

Yes, very true. They should try and see this in person, not on the web or in
Amano's book etc.

>> 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
> to leak.

Yes, good point, you can only eat so much then your full and cannot resorb
anymore. But does this help the algae really?

At some point I would think this would but I think it would be a high level
of leakage (like dying stunted plants, lower DO). Healthy plants likely
don't leak as much or maybe more? I doubt this would be the case since more
healthy plants would indicate that we would have more algae, but we observe
less in these cases, not more algae. So dying or stunted plants, yes ,maybe.
Excess storage and leakage = algae? I do not think so. It doesn't match up
well with observations. I would have horrid algae if this where the case. So
would SFBAAPS. We obviously don't.

>> 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.

I still don't buy that's what's going on in our tanks. In a non CO2 tank
with few water changes okay, this is possible. I'd like a bottle to try out
anyway:). We could sell it!:)

> But if the
> algae can re-establish when extra chemicals become available, then maybe.

Well that's what I've done, add those extra chemicals (nutrients). No algae.
I guess I could take some trimmings and let it rot for a few days then add
the extract to see. I don't think my other half would say yes to this:). She
hated looking at pea soup when I was playing with that.

> 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

Random reason? Elaborate. Say a disturbance?

> 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....

Well this does happen every fall in northern climates and the water gets
nice and rich over the winter. The light limitation kills back almost
everything(algae and plants).

> I  suppose regular water changes together with an experience eye will help.

Yep.

> Neil

Regards,
Tom Barr

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