How to make NO3 and PO4 reference solutions(repost from Left C) - Page 2 - Aquarium Plants

Crazy Loaches · 02-06-2008, 08:18 PM

Quote:

Originally Posted by VaughnH

If you want to use weight instead of volume...

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.

Quote:

Originally Posted by swylie

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?

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.

swylie · 08:34 PM

Quote:

Originally Posted by Crazy Loaches

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.