# Running into PO4 limitation ...



## Milan (Jul 6, 2005)

A question for Edward:

I have done some modifications on my tank and managed to increase the CO2 concentration from 18 to 29 ppm which resulted in, I believe, PO4 limitation. The level of PO4 fell from 0.5 to 0.25, and I noticed some GSA started to form up. My nitrates are @ steady 10 ppm, solely provided by fish load. I've been using NF solution so far, and kept increasing the dosing from 4 to 6 to 8, and for the last few days I'm at 10 ml bi daily, before the PO4 drop.

Now I'm kind of puzzled. Should I further increase the dosing of NF solution, or modify the NPK ratio of the NF to 0.00-0.50-1.00? This would be 11.94gr of KH2PO4 + 29.4gr of K2SO4, .. right? I would like to play this game along without doing WC (perpetual preservation, ..right?).

And, just curiosity wise (I'm not a chemist), 16.63 gr of K in the NPK ratio being 1.00, what weight is it referenced to, making it 1.00? What's the math behind?

Thanks


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## Edward (May 25, 2004)

Hi Milan
You don’t need to modify the solutions. The right way to change the dosing ratios is accomplished by dosing (SS with PF) or (SS with NF). The PPS system was designed on a constant K ratio. No need mixing your own.
You judgment to keep increasing the dosing amount is accurate. For the best result I recommend dosing daily. This helps balanced nutrient uptake. You can increase the NF dosage until you get either PO4 or NO3 deficiency, perhaps both. Then we can go from there. Good game, keep playing. 

Thank you
Edward


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## Milan (Jul 6, 2005)

Thanks for reply Edward.

I do realize there is a constant K ratio in SS, NF and PF solutions (16.63gr/500ml), which allows combining the three, and I practiced that until I had to switch to dosing NF exclusively. But my problem is that I'm constantly low on PO4, even after tripling the initial dosage of NF solution. My nitrates completely come from fish load. This is why I'm thinking about 0.00-0.50-1.00 solution. I don't know how far I can go with increasing the NF without overdosing K. I've heard that gross (what is gross?) amounts of K can interfere with Ca uptake. Mind you, plants are doing fine, pruning every 2-3 days, but the feeling of having low PO4 is like driving a car with a gas gauge needle stuck in red. It still runs, but perhaps I should be looking for a gas station...


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## plantbrain (Jan 23, 2004)

Regarding large amounts of K+ intfereing with Ca uptake=> myth.
A number of folks have shown this to be a myth. Note, we did not prove what the problem was folks where having(I've never seen it nor been able to reproduce the said effect), but it was not due to excess K+ with Ammannia. There is also no support for this effect in the literature whatsoever, only a few salinity stresses when the K+ became very high(200-800+ ppm) and mainly in concentrated solutions or brines, not the water column. Even then, higher K+ helped many plants increase salt stress due to Na+. 

Mg and NH4+ can on the other hand block Ca and there is support for that in the research.

Ca/K+ is only signal feedback mechanism internally in the cell for things like stomatal opening/closing, it has nothing to do with uptake, transport and growth. We had 100ppm of K+, I tested over 60ppm K+ with nothing but excellent growth for Ammannina over several weeks. If it was due to excess K+, the question is why did Erik, myself and others had no such observations?
It cannot be due to excess K+ alone. 

Your test from the fish load source alone maybe flawed. 
Realize that fish add N as NH4 first(do you test for this?), then NO3 secondarily.

So you can have low NO3 and still provide substantial N to the plants.
Plants do not like bouncing back and forth with the NO3 levels, they adapt and get use to a certain NO3 present.
If the NH4 is high, then they use it as quickly as it's produced(typical for most tanks) so gauging how much N is coming into the tank is impossible to test for with a test kit.

There are a couple of back door methods, one is stable isotopes(forget about this one) and the other is measure the amounts of fish food you use and assume it to be like a plant fertilizer.

You can find the N/protein content and you can also add a known weight of fish food typically fed to a 500ml vial and wait to see what your NO3 test kit and NH4 test read.

That will give you a better N budget for the tank.
High fish loads where you no longer need to add N have had issues namely due to the test kit. A well run tank should have a limitation of N and you should need to supplement N with SS.
Even a 120 gal tank with cardinals, cories, and 13 full size discus only got 50% of the tank's total N from fish waste. We used a colorimeter to measure the NO3/NH4. We did not try the fish food in a vial method though.

Still, that is a high fish load(live food, worms etc+ frozen) and the plants still needed more NO3. Unless you have low light 2w/gal or less of PC's, less than say 60% planted, it's unlikely the test is showing you all the information you need to make stay the course on not dosing NO3.

If there is enough NO3, adding NF will drive NO3 uptake. Also, look at your CO2(always) before concluding any changes. This will enhance the method and stabilize a tank far more than any N, P, or K. Basically it will make any method much more flexible and robust. 

Regards, 
Tom Barr


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## Milan (Jul 6, 2005)

Thanks Tom for thoroughly clarifying the K/Ca "issue". Than, correct me if I'm wrong, I should further increase the NF dosage until I see the NO3 drop? Or perhaps, I should do this with SS, or a combination of the two, instead. 

FYI => My tank is 2.2w/g, very densely planted, and the CO2 is @ 29-33 ppm. According to my test, the amonnia level reads 0 ppm.


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## plantbrain (Jan 23, 2004)

I'd bump the CO2 up a tad to be safe, then apply the NF solution.
I'd also check the NO3 test kit and make a solution that matches the range of interest, 10 ppm and a 5 and 15 to make sure.

You can also try bumping the NO3 using the SS to 20ppm and then see how the nutrient decline responds. You likely should see a decline where at 10 from fish waste, you weren't. The inorganic fractions are bioavailable, sometimes, and it's not an easu thing to answerm, the organic fractions are not particularly labile, but take more time to break down, but most test kits reduce the total NO3, not just the inorganic fraction.

In any event, you can add more inorganic NO3, and it's no big deal since you can add the NF solution to make it drop back down. I dount you have enough fish to max out the N is my point. I'd be surpised, very, if that was the case.
Something else is up, either CO2, or the type of NO3 or the test kit. 
Check those first. And I typically add more CO2 if anything seems odd but not so much to cause fish issues so you need to watch them and be around the tank later in the day(last few hours) after you change the CO2. Do it slowly.

PPS seems to work pretty good once the CO2 is cranked up, same with EI.
If not, things can go sour depending on how far off things might be with CO2 and folks end up looking at the N or P etc instead of the CO2.

Anytime you see a strange lull in uptake or growth, test kits seem off etc look at CO2, then look at it again and add more.

Regards, 
Tom Barr

www.BarrReport.com


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## Milan (Jul 6, 2005)

Tom, I'm already @ 30-ish ppm with CO2. Wouldn't more be beyond plant's even luxury uptake? Anyhow, I'm on DIY, and it took quite a bit of a challenge to get it up to this level. I don't think it would go any further without either switching to pressurized or doing some design gymnastics again. It's simply not practical for me at this point, ... time and money wise.

That leaves me with two choices, according to what you are suggesting. Either further increase NF dosage, or use SS to get NO3 to say 15-20 ppm, and see how things are progressing.

What would be your preference?


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## plantbrain (Jan 23, 2004)

I'd personally try SS to 15-20ppm.

While no water changes are a goal for many, you can avoid high levels NO3 and re set the tank also, then have a better handle at the issue by isolating it and removing some unknowns as the NO3 present(10ppm) that is just sitting there.

DIY CO2 is variable and can cause issues, namely declines in production due to temp changes, time since last brew change etc. 
So while I may measure 30ppm today at 9pm, the CO2 in the morning may only be 10ppm, then later in the week may max out at 12ppm.

It's so worth getting gas tanks.
Assuming the CO2 is good, the test kits are perhaps accurate, the NO3 from the SS should kick the uptake for the other nutrients => N&P.

You should see a rather fast decline, within 1-2 days of both NO3 and PO4.

Regards, 
Tom Barr

www.BarrReport.com


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## Milan (Jul 6, 2005)

Thanks Tom! Will do as suggested ..

BTW, I wish I could squeeze out a gas tank from my aquatic budget, but my wife says I've already exsausted it ... No way of convincing women ...[-X


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## MatPat (Mar 22, 2004)

Milan said:


> BTW, I wish I could squeeze out a gas tank from my aquatic budget, but my wife says I've already exsausted it ... No way of convincing women ...[-X


That's why we just have to do it anyways and face the consequences later


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## Milan (Jul 6, 2005)

Takes some courage for a peaceful guy ...


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## Edward (May 25, 2004)

Milan,
You need to check the NO3 and PO4 test kits first. See FAQ or PPS documentation. Then, if you still have high NO3 dose more NF daily until you see some PO4. You can not overdose K, the solution is balanced. 
This will put your aquarium in order.

Thank you
Edward


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## Milan (Jul 6, 2005)

Edward said:


> You need to check the NO3 and PO4 test kits first. See FAQ or PPS documentation. ...


Thanks Edward!
I believe you are referring to calibration, ..right? I've never calibrated my tests, simply because I used volumetric measures to make my solutions, and never bothered with extreme accuracy ... I'm not saying I dumped powders in there like my grandma making cookies, just that it was as accurate as it could be. Say, down to a 1/4ml. 
However, I did a substantial WC yesterday, tested NO3 and PO4 afterwards and they both read 0 (zero). Then I started adding SS and today, after two doses of 20 ml they are approximately 10 and 0.75 ppm. Although this may be a coincidence, this matches the N to P ratio in the solution., giving me some confidence in my tests and solutions.

So I guess, I keep fertilizing with SS, until I see the two splitting apart, and then introduce the NF in the equation ... Right?


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## Edward (May 25, 2004)

Hi Milan
We used word calibration before that scared some people. This simple procedure is not about extreme accuracy. We should have called it a confirmation or verification. Testing known solution verifies test kit proper operation and user readings. Some test kits have wrong colour charts and some have switched sea with fresh water charts.



Milan said:


> I'm not saying I dumped powders in there like my grandma making cookies &#8230;


&#8230;that would be the EI.

You can always switch the solutions and select what makes your aquarium stable. The PPS line is made of three fertilizer solutions SS, PF and NF offering flexibility to fit any aquarium requirements.

Thank you
Edward


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