Scale choices for measuring reef chemicals?

Cory · Jan 9, 2015

The scale I currently have only measures 1g each increment. That seems not good enough. I just bought a new scale that has a precision of .01g. My concern is it only weighs a maximum of 500g. Would this be good enough for Randy's home made calibration solutions?

JimWelsh · Jan 10, 2015

I have two scales. One is an old-school Ohaus Triple-Beam Balance, with a 500g capacity, and 0.1g resolution. The other is an inexpensive electronic balance with a 300g capacity and 0.01g resolution. I use the Ohaus for my DIY two-part measurements, because it has sufficient capacity, and more than sufficient resolution for the job at hand.

Randy Holmes-Farley · Jan 10, 2015

Cory said:
The scale I currently have only measures 1g each increment. That seems not good enough. I just bought a new scale that has a precision of .01g. My concern is it only weighs a maximum of 500g. Would this be good enough for Randy's home made calibration solutions?

If you mean the salinity solutions, it is perfect for that!

Cory · Jan 10, 2015

Thanks guys!

Id like to know if I can weigh the water part of salinity solution as many times as needed? Will it still be accurate? (For total volume)

JimWelsh · Jan 10, 2015

Randy Holmes-Farley said:
If you mean the salinity solutions

I need to learn to read more carefully! :tongue:

Randy Holmes-Farley · Jan 10, 2015

Cory said:
Thanks guys!

Id like to know if I can weigh the water part of salinity solution as many times as needed? Will it still be accurate? (For total volume)

What exactly do you mean? Why do you need to weigh it more than once?

Skydvr · Jan 10, 2015

I think he means for larger volumes as he is limited to 500g at a time.

If so, with the +/-.01g accurcy, if you were to measure out 5,000g, you would be at a +/-.1g accuracy, which would still be fairly reasonable.

Randy Holmes-Farley · Jan 10, 2015

I agree, but if we are still talking salinity standards, 500 mL is enough for most uses except perhaps a floating hydrometer.

Cory · Jan 10, 2015

Hey guys, what I mean is If I want to weigh the water for the refractometer standard is something like 2100g (IIRC) of water can I just weigh 500g (the maximum my scale goes to) 4.1 times? Any concerns with weighing the water more than 4 times. My concern comes from Randy's comment in his article saying that a 2 liter coke bottle can vary in volume.

Randy Holmes-Farley · Jan 11, 2015

OK, that is fine, but as mentioned above, the total uncertainty is the addition product of each weighing. Still fine using a 0.01 g scale.

But unless you need a lot of it, I would make it on a smaller scale.

Since the refractometer standard is exactly 36.5 weight percent NaCl, use 3.65 grams of NaCl and 96.35 grams of pres fresh water.