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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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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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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.
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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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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Re: Results 8/31/08

NO3 23 ppm
PO4 0.4 ppm
K 10 ppm

I'm going to break away from the PPS Stock plan and go to the NO3 free plan until my NO3 goes down.

If I can figure out how to edit my posts, I'll revise the chart!

I realize that there are people, like Hoppy with green thumbs as long as an arm, who can just smell an aquarium and know what is going on. (That was meant to be a sincere complement). Unfortunately, I can only see numbers and the test result say that for me at least, there is no way to figure out what is going on my your tank with out testing it on a regular basis.

Maybe someday I'll be as good as Hoppy without doing any testing.

BTW: I've almost figured out how to take photos of my aquarium. Unfortunately the colors are all mixed up. When I get that squared away I'll post some pics.
Wow, do you have me figured out wrong! I struggle as much as anyone trying to get good plant growth with little or no algae growth. My skills at judging what is wrong by looking at plants are almost non-existent, which is why I use the EI method. I appreciate the compliment, but it is aimed at the wrong person. (My thumb is black - I'm an expert at growing BBA)
 
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