Accurate measurements - The Planted Tank Forum
 
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post #1 of 8 (permalink) Old 05-04-2005, 03:37 PM Thread Starter
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Accurate measurements

Thought I'd post the results of some testing I conducted. This is related to my offers here.

I took a sample of water from my betta tank (1.5gal, duckweed infested) before a water change, after a 25% water change and addition of fertilizer and traces, and a sample of the tap water used for the change. I analyzed for Na, K, Ca, Mg, Cl, NO3, and SO4. Here are the results (tap, then pre-WC, then post-WC, in parentheses is the value reported by my municipal water supplier if available)


Na+: 9.5, 23.3, 25.3ppm (16)
K+: 2.5, 22.4, 34.5ppm
Mg+2: 2.2, 3.9, 7.4ppm
Ca+2: 15.3, 16.7, 17.4ppm
Calculated total hardness (GH) from above values: 47.5, 58.1, 73.9ppm (56)
Cl-: 25.3, 50.6, 57.8ppm (20)
NO3-: Not detected, 15.6, 17.0 (0.38 maximum over 1 year)
SO4-2: 51.8, 120.5, 144.9ppm (35)

After the water change I added: a "squirt" of Kent Freshwater Plant, a few crystals of Epsom salt (MgSO4*7H2O), and a few crystals of KNO3.

So a couple of obvious questions: 1. Why is the sodium so much higher in the tank? Well, I looked at the ingredients on the Kent and it contains both sodium-EDTA and sodium molybdate. I assume these are the main sources.

2. Why is the chloride higher in the tank? Again Kent includes muriate of potash which is KCl. It also contains cobalt chloride.

The higher sulfate and magnesium are due to the Epsom salts, while potassium is due to both the Kent and the KNO3.

I'm still trying to develop an easy test to differentiate and measure Fe+2/Fe+3 as well as a better phosphate test. The above was the result of a capillary electrophoresis separation with indirect UV detection.

It is nice to know my tap K+ value as well as the resulting conc. in the tank - it verifies my dosing levels. Also, the nitrate is much more precise than the colorimetric, so no guessing "is that 5ppm or 10ppm?"

Fun with chemistry (and instruments)!

Kevin

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post #2 of 8 (permalink) Old 05-04-2005, 04:27 PM
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So here we have the two extremes the "EI" where you don't care about current levels, and the "AAS" where you measure each atom to get an absolutely exact number.

I am kind of in the middle, I would like to know what my K and Fe is, but I can live without it, and approximate results of N and P testing are sufficient, although it would sure be nice to know exactly (without having to pay, heh).

Thanks for your offer... interesting to see the Na and Cl amounts, as well as the K (isn't it a little high? Some have reported problems with high K levels in soft water, but then, nobody knew how high they really were).


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post #3 of 8 (permalink) Old 05-04-2005, 06:20 PM Thread Starter
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Quote:
Originally Posted by Wasserpest
So here we have the two extremes the "EI" where you don't care about current levels, and the "AAS" where you measure each atom to get an absolutely exact number.

I am kind of in the middle, I would like to know what my K and Fe is, but I can live without it, and approximate results of N and P testing are sufficient, although it would sure be nice to know exactly (without having to pay, heh).

Thanks for your offer... interesting to see the Na and Cl amounts, as well as the K (isn't it a little high? Some have reported problems with high K levels in soft water, but then, nobody knew how high they really were).
Yep, this is definitely an extreme. I have to admit I'm not going back and "tweaking" levels to anything very specific - after all, this is a tank with duckweed!

The K and nitrate are a little high - mostly due to my highly accurate dosing methods of "squirts" and "few crystals". This is only a 1.5gal duckweed/betta tank, so I don't dose very precisely.

This also relates to how reliable your water supplier numbers are - there is quite a difference in the sodium (-40%) and sulfate (+48%) levels. Since they measure "at the plant" and I measured "at the tap", and we measured at different times, the difference is not unexpected.

I don't plan to have "regular customers" out of this - just people trying to get a handle on EI or other dosing schedules or to check their tap water more formally. After all, I'm not going to make a living with the prices I'm offering

Kevin

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post #4 of 8 (permalink) Old 05-04-2005, 11:02 PM
 
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Just out of curiousity, I may have a sample of my tank water tested "professionally" similar to what you're offering.

Since I don't envisage sending you a water sample from here for testing, I thought I'd try to contact a lab or something here and see if they would do it and for how much.

Question is, what are the different testing methods that I should be looking for (besides the hobby kit color system)? Which gives the best "value for money" in the sense that it gives accurate results but doesn't require hundreds of dollars to do?
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post #5 of 8 (permalink) Old 05-04-2005, 11:27 PM
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My multimeter does just fine with NO3 to an accuracy of +, - 0.1ppm of NO3 over a 0-30ppm range.

Fe to about 0.003ppm

But total Fe does not tell you much...........it does not tell you bioavailability.
we use AAS for copper and we can use it for Fe, but we have little need in weed control for Fe testing.

The NH4 is accurate to about 0.01ppm, not bad.

Given these ranges, I'm plenty happy enough and few if any planted aqurist will ever get anything out of such close tolerances. You simply do not need to have such accuracy for this hobby.

This is a good thing.

If I maintain and range of NO3, say at 15ppm +, - 1ppm.... I have to dose it frequently to maintain this, like 3-4x a day on some tanks, while a non CO2 might take 2 days per dose.

The end result vs adding NO3 every 2-3 days and having a wider range, say 10-20ppm, is far more practical.

Do you gain anything from 15ppm(+, -) of NO3 vs 10-20ppm?
Not in terms of plant growth/biomass.

Excess is still excess.

If you want more and more accuracy, at some point there is a need to realize it will no logner help, if you are sending a space craft to hit a small region is space, you need high accuracy.

We sure don't though..........

Regards,
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post #6 of 8 (permalink) Old 05-08-2005, 06:42 AM
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Quote:
Originally Posted by plantbrain
My multimeter does just fine with NO3 to an accuracy of +, - 0.1ppm of NO3 over a 0-30ppm range.

Fe to about 0.003ppm

But total Fe does not tell you much...........it does not tell you bioavailability.
we use AAS for copper and we can use it for Fe, but we have little need in weed control for Fe testing.

The NH4 is accurate to about 0.01ppm, not bad.

Tom Barr

Just curious, I'm not about to buy one, but what brand and approximate cost is a "multimeter"?

Also, when I first bought my house, I had our well water tested. Back then, I knew almost nothing about water chem... I think I might have it tested again. The test was free through a water company which sells bottled water and water treatment equipment. If that doesn't work out, I might take Kevin up on the offer. Seems fair enough to me. Thanks, bob





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post #7 of 8 (permalink) Old 05-09-2005, 07:46 AM
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Quote:
Originally Posted by Betowess
Just curious, I'm not about to buy one, but what brand and approximate cost is a "multimeter"?
About 1200$
Lamotte and other companies make them, Hanna makes ion specific
meters, so you could test say NO3 at a 0.1ppm accuracy over a 0-30ppm range for 170$. But that is the only parameter you can measure for that price.

Regards,
Tom Barr



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post #8 of 8 (permalink) Old 05-09-2005, 07:59 AM
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Kevin, what you will want to do is take samples from a test tank(as series of 6-20 would be ideal with the same plant) for each day during a week or 3 week peroid and measure the inuts and outputs in order to get the rate.

The rate is far more useful that any static measurement.
Then you may use this to predict what your tank needs, thus much less/no testing thereafter.

If you spend the effort, work, time and $ on something, get something useful out of it rather being a slave to the testing device.

The rate is useful.

This same approach is useful for daily CO2 levels.

Measure the level over a time peroid during the day and night when growth is good.

The when growth is bad(induce this if you want through PO4 limitation etc)
do the same type of measurements.

Then you can also measure the O2 levels at the same time.

These are basic things to test for, but few have ever done them in aquariums.

Instead taking only a few readings once a week or so.
there are many trends folks do not see over a week that they might if test were taken daily or hourly with the case of CO2 and O2.

That's a lot of testing, but it's not a long time peroid, typical test peroids are 1 to 3 weeks to get a rate.

You might consider these notions and give them a try when testing.
I fully encourage testing, but at a much higher level and with much more care than what the past has done for the hobby.
Then we can really look at things much better and focus on the needs of the plants.

Regards,
Tom Barr



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