How to make NO3 and PO4 reference solutions(repost from Left C)

Hey Tom, doesn't it makes 20ml of a 20ppm solution?!?

We have a 1000ml of a 1000ppm solution, so taking 2ml of it and adding to 18ml of water there should be a 20ppm solution, not a 100ppm solution...
Is it right?!?
Thanks Tom!
Bye!

 

hehehe
Yeah, I've got the wrong calcs in here...
I refeered 2ml as 200ppm of the solution (don't know the hell why I did it!), but it's still a 1000ppm solution, this 2ml added to 18ml would really be 100ppm! (simple division as it said in the case of 1ml for 9ml)
I messed the whole thing! hehehehe
Thanks again Tom!
Bye!

 

Just curious if there is a guide based on the use of things like teaspoon, etc... I have a gram/ounce postal scale (up to 5#) but unfortunately it is not accurate enough for this kind of precision. I dont mind if it requires the use of a larger amount of water to get more accuracy (I know its hard to dose 1/64 of a teaspoon or something like that!) but a couple of gallons of DI water from wallmart for 59c is cheaper than buying a new scale.

 

So I take it thats a no then on using volume for measurement as opposed to weight.

 

If you want to use weight instead of volume I suggest weighing about 10 teaspoons of each fertilizer, then dividing the weight by 10 to get the weight per teaspoon. The accuracy you could get this way would be limited, partly because measuring spoons are not very accurate. I have maybe 4-5 sets of measuring spoons made of different materials, by different manufacturers. If you have that too, measure a teaspoon using each of those, weigh the total weight of them and divide to get a slightly more accurate weight per teaspoon. Or, to get perhaps a little more accurate, measure using the half teaspoon, teaspoon and tablespoon (3 teaspoons), and do the same.

But, of course, as soon as you buy some more KNO3, KH2PO4, etc. the weight per teaspoon will likely be at least a little bit different.

 

I guess it depends on how precise you want your calibration solutions to be. There's no need for them to be any more precise than the color key that comes with your test kit unless you're using a spectrophotometer.

If you're feeling really thrifty and have a loose sense of ethics you could certainly buy a digital kitchen scale at Target or Walmart, use it, and then return it. Those scales can be precise to the gram. You only need to make a reference solution once, right?

 

Other way around, but thanks for the tips, that might actually work out, just takes some extra testing. I do already have weight per cup measurements, I've calculated out about how many pounds of ferts I would need for a year at my current dosing.

I know exactly what you mean, and I've never done anything like that before

But as I stated I have a gram-accurate scale. What this is calling for looks to need maybe a hundredth of a gram sensitivity. I could go out and get a new scale its not really a money issue I guess, I just feel like it’s a waste since I already have a scale that I rarely use, now I would have two.

I guess volume is simply more variable than weight for a reliable measure? If were taking about not using volume because its only marginally more inaccurate than couldn’t we use a larger sample like I mention with a gallon jug of DI water? Lets say what we need happens to be very small and hard to judge by volume, like 1/32 tsp. So then take a larger sample like 1 tsp, put it in a gal, then using something accurate like a 10ml syringe, extract 10 ml out (or whatever it would be to get back down to the 1/32 tsp figure) and start your actual solution. Unless volume is just a lot more variable than I realize.

 

Shows how much I pay attention... The gentleman already has a scale. Hmm... Well, in that case, consider using the scale to measure your water. At standard temperature and pressure water weighs 1 gram per ml, and your scale is probably much more precise than a gallon jug or a nalgene bottle or glass measuring pitcher. A 10 ml syringe is probably better than measuring 10 grams of water on the scale though.

Your idea of using larger masses and then diluting the samples is called "serial dilution" and it's definitely the best way forward. You can make very precise dilutions with a method like you described, and it allows you to measure in reasonable units: 10 ml, 100 g, etc. I'm sure Tom does serial dilutions in his sleep.

If you use the tools you have and the techniques you described you'll be able to make a reference solution that's more precise than your test kit.

Just remember that a 1:10 dillution is 10 ml + 90 ml = 100 ml, not 10 + 100.

 

I revised the making NO3 and PO4 reference solutions article that I did a while back. The latest one only requires scales that will measure to two decimal places instead of three like the older version. Also, all you need is one liter of distilled water to make both reference solutions. Here it is:

Directions for Making NO3 and PO4 Reference Solutions III


You will need the following:
- 1 liter of distilled water
- 500 mL graduated cylinder
- 50 mL graduated cylinder
- 1 mL or 3 mL pipette or another measuring device to measure small mLs of solutions
- Scales that are accurate to two decimal places
- KNO3 and KH2PO4 dry fertilizers


Here's a way to make 10, 20, 30, 40 and 50 ppm NO3 reference solutions:

Add 0.70 grams of KNO3 to 429 mL of distilled. This makes a 1000 ppm NO3 solution. (It's really a 1000.72 ppm NO3 solution.)

Add 2 mL of the 1000 ppm solution to 18 mL of distilled water. This makes 20 mL of a 100 ppm KNO3 solution.

Add 15 mL of the 100 ppm solution to 15 mL of distilled water. This makes 30 mL of a 50 ppm KNO3 solution.
* Note: You can use this for the 50 ppm NO3 reference solution.

To make a 10 ppm NO3 solution:
Add 2 mL of the 50 ppm solution to 8 mL of distilled water. This makes 10 mL of a 10 ppm NO3 solution.

To make a 20 ppm NO3 solution:
Add 4 mL of the 50 ppm solution to 6 mL of distilled water. This makes 10 mL of a 20 ppm NO3 solution.

To make a 30 ppm NO3 solution:
Add 6 mL of the 50 ppm solution to 4 mL of distilled water. This makes 10 mL of a 30 ppm NO3 solution.

To make a 40 ppm NO3 solution:
Add 8 mL of the 50 ppm solution to 2 mL of distilled water. This makes 10 mL of a 40 ppm NO3 solution.



Here's a way to make 0.1, 0.2, 0.5, 1.0, 2.0, 3.0, 4.0 and 5.0 ppm PO4 reference solutions:

Add 0.70g of KH2PO4 to 489 mL of distilled water. This makes the 1000 ppm PO4 solution. (It's really a 999.04 ppm PO4 solution.)

Add 1 mL of the 1000 ppm solution to 9 mL of distilled water. This makes 10 mL of a 100 ppm PO4 solution.

Add 2 mL of the 100 ppm solution to 18 mL of distilled water. This makes 20 mL of a 10 ppm PO4 solution.

To make a 0.1 ppm PO4 solution:
Add 1 mL of the 10 ppm solution to 99 mL of distilled water. This makes 100 mL of a 0.1 ppm PO4 solution.

To make a 0.2 ppm PO4 solution:
Add 1 mL of the 10 ppm solution to 49 mL of distilled water. This makes 50 mL of a 0.2 ppm PO4 solution.

To make a 0.5 ppm PO4 solution:
Add 1 mL of the 10 ppm solution to 19 mL of distilled water. This makes 20 mL of a 0.5 ppm PO4 solution.

To make a 1.0 ppm PO4 solution:
Add 1 mL of the 10 ppm solution to 9 mL of distilled water. This makes 10 mL of a 1.0 ppm PO4 solution.

To make a 2.0 ppm PO4 solution:
Add 2 mL of the 10 ppm solution to 8 mL of distilled water. This makes 10 mL of a 2.0 ppm PO4 solution.

To make a 3.0 ppm PO4 solution:
Add 3 mL of the 10 ppm solution to 7 mL of distilled water. This makes 10 mL of a 3.0 ppm PO4 solution.

To make a 4.0 ppm PO4 solution:
Add 4 mL of the 10 ppm solution to 6 mL of distilled water. This makes 10 mL of a 4.0 ppm PO4 solution.

To make a 5.0 ppm PO4 solution:
Add 5 mL of the 10 ppm solution to 5 mL of distilled water. This makes 10 mL of a 5.0 ppm PO4 solution.



Left C

** Added at Johnathan's request 10-3-13

 

Wow! Having two different methods for making reference solutions together is a terrific idea.

 

Are these reference solutions like the CO2 4dKH reference solution?

Im sorry if this question is stupid to others but i'm just curious. I was reading the EI target ranges posted by Tom and I would like to know if my tank (55g) is within range. I already have a nitrate and phosphate test kit which comes with a color coded chart to read the levels in the water.

So are the reference solutions mentioned in this thread meant for color comparison like the 4dKH solution? I'm lost sorry

And if the the purpose of EI is to have an unlimited amount of nutrients for the plants to use throughout the week, then why be concern about having a NO3 range of 10-30ppm and PO4 of 1.0-2.0 ppm? Are these the optimal ranges?

Thanks.

 

I'm sorry I just don't understand the next step after making the reference solution. Are we to run two test each time, for example, have the reference solution and the water tank in separate 5mL cylinders and do the test to compare colors?

Thanks.

 

You follow the test kit's direction for testing your aquarium water, if that is what you are testing. If you are testing your tap water, same thing, just follow the directions. Let's call this the sample.

Then the reference solutions are made using "pure" compounds and "pure" water. These give you various color references. Then you compare your sample's color to the reference's color to get an idea of your sample's concentration. It is better to do more than one sample. Do 2 or 3 samples to make sure that the samples are made correctly. If your samples turn out to be different colors, you know that there is an error somewhere. Then you need to find out what is wrong. If all 2 or 3 samples are the same color, you know that either they are made correctly or you made the same, exact error each time.

Make sense?