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Discussion Starter · #1 ·
OK for those of you who are interested in what happens to K. I received my test kit from LaMotte and did my first test Sunday 7/6. After 10 days doing PPI here are my tank results:

N03: 6 ppm
P04: 0.2 ppm
K: None detected

My plants were showing the effects of low K so I added suficient K to bring my level up to 10 ppm.

Any suggestions on how often you'd like to see tests results?

BTW I'm going to get Fe and CO2 test kits as well.
 

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Does this mean the potassium you were dosing, presumably the K part of the KNO3, was all taken up by the plants and/or adsorbed by the substrate? (If the substrate material has a reasonable CEC it should adsorb some potassium.)

I suggest adding some or more K2SO4 to the PPI formula, dosing for ten days, and rechecking for potassium. Repeat that until you get a measurable value. Then dose that mix for a week or 10 days and re-measure potassium, repeating several times, to see if it accumulates and how fast.
 

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Discussion Starter · #3 ·
Additional details

On 7/6 I checked my water and found that there was no detectable K; so, I added sufficient K to bring the level up to 10 ppm. On 7/8, I rechecked the level and K was at about 8ppm.
I can see a noticeable improvement in plant growth since 7/6 as well as an increase in algae growth.
I add the PPS recommended levels of nutrients daily and replace about 20% - 30% of the water, weekly. I add the equivalent of 20 ppm of CO2 each morning as well as the recommend amount of Flourish Excel.
 

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Discussion Starter · #4 ·
update on KPN levels

OK here are the KPN levels after 17 days on PPS

K none detected
PO4 0.2 ppm
NO3 7 ppm

Added K again to bring level to 12 ppm

It appears that after 17 days nutrient consumption is limited by available K.
 

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Discussion Starter · #6 ·
Re: update on KPN levels

Not exactly true because K is a mobile element. Plants do take more of K then they actually need so assuming a deficiency from testing K excess is probably misleading.
I agree that K is a mobile element in the fact that it is not incorporated into the structure of the plant and is constantly being exchanged for other K outside the plant. But from my understanding of cellular biology it doesn't seem possible for a plant to take in more K than it needs.

Cellular levels of K must be in a very narrow range for cells to function properly. Plants have biochemical mechanisms that "pump in" and "pump out" K. They can concentrate K from the environment using "pumping in" mechanisms. As the level of cellular K increases, the "pumping out" mechanism starts up. Eventually, the "pumping in" and "pumping out" mechanisms are in balance and the level of K remains constant in the cell.

As long as the plant volume is constant, the level of K in the plants and aquarium water will be the same. As plant volume increases, more K is required and is removed from the tank water.

It may be that my plants have been suffering from a long term deficiency and the amount of K being taken up is just bringing the cellular level back to normal. If that is true then K consumption will eventually decline. I'm interested to see what happens.

BTW. My notion that growth is limited by available K is not unique. There are a large number of aquatic plant fertilizers on the market that supply only K, Fe and trace elements.
 

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Hi ray-the-pilot,

Very interesting thread, please keep us updated as your analysis continues!
 

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Discussion Starter · #8 ·
Weekly update:

K 15 ppm
PO3 0.3 ppm
NO3 7 ppm

It looks like the extra K that I added over the last two weeks has finally been incorporated into the plants.

I did an extra 10% water change and will try one or two more during the week.

Over the weekend I made some changes to my tank.
1. Did some aggressive algae control including removal from glass and driftwood.
2. Added 6 more Oto Cats (total of 11)
3. Added 3 Siamese Algae Eaters
4. Added 15 Cardinal Tetras.
 

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Discussion Starter · #10 ·
OK here is the weekly update:

K 15 ppm
PO3 0.3ppm
NO3 10 ppm

Here are the details.

Because of visitors, I was unable to do any water changes this week end.

After reading about the toxic effects of gluteraldehyde, I decided to stop using Flourish Excel. Maybe I’ll automate CO2 additions. I have to figure out a way to measure the CO2 added. Anyone have a suggestion.

Subjectively, my tank seems in really great condition although I’m starting to worry about too little algae (yes, I’m worried about starving out my algae eating army).
 

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This has been very interesting to me. I recall that your original question or comment about potassium was about whether it would continue to build up since the plants don't actually consume it like they do nitrates, for example. Have you reached any conclusions about that?

There are only two usable methods for measuring how much CO2 is in the water, that I know of. One is to spend around $2000 on a piece of equipment that measures it directly and very accurately. The other is to use a drop checker, as described in http://www.aquaticplantcentral.com/...aquarium-projects/32100-diy-drop-checker.html, which gives usable results, but not extremely accurate results.
 

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Discussion Starter · #12 ·
I don’t think I can make any solid conclusions. One thing I have learned is that it is hard to determine the levels of chemicals in your water without testing for them.

Once I got my K level up there seemed to be a sharp drop in algae growth. This could also have been due to increased consumption from the added algae eating fish. (This is called a poorly controlled experiment).

My plan is to do additional water changes this week to bring the level of K and NO3 down. I will continue to do the daily additions of macro/micro nutrients.

Since the daily addition of K/PO4/NO3 is approximately 1/.1/1 it seems from the current levels that PO4 is being used more rapidly (in my tank). I’d like to get my tank water to a K/PO4/NO3 level close to 1/.1/1. Then I could get a better grip on how the K/PO4/NO3 level changes with time.

You’ve probably guessed that I have a chemistry background so this has been a lot of fun for me.
 

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Tom Barr tells us that the best way to adjust the growth rate in an aquarium is with the light intensity. Next best, is with nitrate, although this is a distant second. His EI method is aimed at always having the tank non-limited by any of the nutrients, and his typical K/PO4/NO3 dosage is more like 1/.25/1 than 1/.1/1. I think he does this because a shortage of phosphate will become the limit on plant growth and that isn't desirable at all. You might enjoy visiting his forum at http://www.barrreport.com/barrreport.php and discussing this with him.
 

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There is a chart based on pH and KH that will give you CO2 concentrations. I'm not at home and dont have access to it but if I remember I will attach it tonite.
 

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There is a chart based on pH and KH that will give you CO2 concentrations. I'm not at home and dont have access to it but if I remember I will attach it tonite.
That chart is based on the equation that relates CO2 concentration to pH and KH, but it is only applicable to water which has no source of alkalinity or acidity other than carbonate and carbonic acid. Our aquarium water rarely fits that criteria, so the chart almost always gives much too high a concentration of CO2 than actually exists in the aquarium.

The concentration of CO2 in water is proportional to one over ten raised to the pH power, so even slight errors in pH, such as by having pH affected by tannins, or phosphates, will badly distort the calculated concentration of CO2. (A change in pH by 1.0 - say from 7 to 6 - results in a change in concentration by a factor of 10 - say from 2 to 20 ppm)

The fact that this chart is published everywhere, in many websites, in books, in magazine articles, etc. doesn't mean it is a good CO2 measuring method. Believe it or not, "everyone" has often been wrong.
 

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Discussion Starter · #16 ·
Here is the update for 8/3/08

K 12 ppm
PO4 0.4 ppm
NO3 12 ppm

There is almost no algae in my tank; so, I’ve started to supplement my fish feeding with algae tablets. In the past my Oto’s have ignored them but faced with starvation they may think otherwise.

I’ve changed my fertilization plan temporarily. I’ve stopped using the standard PPS stock solution and started using only a KHPO4 solution that provided the same level of PO4. I’ll continue to do this until I get closer to the stock solution ratios of K/PO4/NO3 = 1.4/0.1/1.

I am doing about 20% water changes per week.

I’ve upped my lighting to max!
I have 2 x 65 watt Sunpaq 6700 K /10,000K CFL on 12 hours/day and
1 x 150 watt Coralife 6700K HQI on 6 hours/day.
The HQI is about 16” above the tank to reduce intensity.

I’m adding 4 gm CO2 daily (equivalent to 20ppm for my tank).
 

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Discussion Starter · #17 ·
Tom Barr tells us that the best way to adjust the growth rate in an aquarium is with the light intensity. Next best, is with nitrate, although this is a distant second. His EI method is aimed at always having the tank non-limited by any of the nutrients, and his typical K/PO4/NO3 dosage is more like 1/.25/1 than 1/.1/1. I think he does this because a shortage of phosphate will become the limit on plant growth and that isn't desirable at all.
Everyone has their own formula!

I am using the schedule recommended for PPS:

In 1 liter bottle:
59 grams K2SO4 (Potassium Sulfate)
65 grams KNO3 (Potassium Nitrate)
6 grams KH2PO4 (Mono Potassium Phosphate)
41 grams MgSO4 (Magnesium Sulfate)
Fill with distilled water and shake well. Let sit overnight.

Dose 1 ml of each solution per ten gallons of tank size.

When I chug this through the fertilator I get the following daily increases:

K 1.41 ppm
PO4 0.11 ppm
NO3 1.05 ppm
Mg 0.11 ppm

This agrees with my own spread sheet.

BTW your question about the ratio of PO4 made me go back to my own spread sheet and I found a mistake in my calculations for K2SO4, which I fixed.
 

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Here is a link to the chart I use. It has been adjusted for the inaccuracies others have pointed out unless you have abnormally high phosphate levels and/or other buffers in which case it wont work. The same inaccuracy existes for CO2 test kits i.e. they can be thrown off by buffers. Also, a drop checker can only tell you if you are Low, OK or High - not where you are within each range which can vary considerablely.

http://www.csd.net/~cgadd/aqua/art_plant_co2chart.htm

........sounds a bit like someone has some kinda beef or got out of the wrong side of bed today..........
 

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Chuck Gadd's website clearly says his chart and his built in calculator, which is a very nice one, are based on: "The formula used for this calculation is: CO2 (in PPM) = 3 * KH * 10( 7-pH ) where KH is Carbonate Hardness in degrees." This is the standard equation relating CO2/ph/KH, with no corrections at all. Chuck also makes it pretty clear that you can't have phosphates in your water, which most water companies add routinely to keep the pH above 7 to avoid copper piping erosion. And, it follows that anything else in the water that affect the pH, such as tannins or other acids, will also make the equation invalid.

Recently Tom Barr purchased a $1500 instrument that really does measure the concentration of CO2 in the water, independent of pH and KH and other pH affecting substances, accurate to something like +/- 2 ppm, as I recall. He was surprised when he used it to find that he had much less CO2 in his tank water than a drop checker was telling him, and the drop checker gave less CO2 in the water than the pH and KH would tell him. Measuring the concentration of CO2 in water is a very difficult job.
 

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Discussion Starter · #20 ·
Recently Tom Barr purchased a $1500 instrument that really does measure the concentration of CO2 in the water, independent of pH and KH and other pH affecting substances, accurate to something like +/- 2 ppm, as I recall. He was surprised when he used it to find that he had much less CO2 in his tank water than a drop checker was telling him, and the drop checker gave less CO2 in the water than the pH and KH would tell him. Measuring the concentration of CO2 in water is a very difficult job.
Actually, measuring CO2 in water is an interesting discussion. Do you think we could move it somewhere else where it is more appropiate? I'd add my two cent there.
 
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