another salinity meter option

[rwb500]

A while back I posted about a pen-style salinity meter that was a lot cheaper than the Pinpoint model, but the quality was questionable. Now I have found another one, this time made by Amprobe, a very reputable instrument manufacturer. They have a no-questions-asked warranty.

It's called the Amprobe WT-30 and can be found all over the web for about $80 shipped. Only a little less than the Pinpoint, but it's probably higher quality. Its also only a little more than a quality refractometer. I plan on keeping my old busted refractometer as a back up and getting this instead of buying a new refractometer. I'll post back here when/if I get mine, although I'm quite sure it will perform as advertised.

datasheet:
http://content.amprobe.com/DataSheets/WT30.pdf

let me know what you guys think.

 

[bertoni]

It claims accuracy within about 0.8 ppt for saltwater, which probably is good enough. Personally, I'd spring for the PinPoint, since it seems to be much more precise for the range we are targeting, but the Amprobe does cover a much wider range, if that's of interest.

 

[rwb500]

well, i couldn't find any precise information on the accuracy of the pinpoint monitor. I dont think its likely that the hobbyist grade device would be better than the scientific equipment with published accuracy ratings.

i got my WT-30 in the mail today and it is pretty nice to use. it displays the temperature simultaneously so water changes have never been easier. However, it does take a while to "get going." the manual says something about waiting a few minutes while the device is in the solution, and right after turning it on, and placing it in my water, it takes a few minutes for the reading to climb up to where it stays. but after that, moving back and forth between RO water, tank water, and my new salt mix, the readings are instant. I havent yet determined if the unit just needs to be on for about 5 minutes, or if it needs to be in a salt solution for 5 minutes, to be "warmed up."

I'll post a follow up in a few weeks when I have some more experience with the device. then i'll know enough to recommend it, or recommend against it.

 

[jcw]

The pinpoint model's readings also takes a couple minutes to stabilize. Annoying, imo.

 

[Randy Holmes-Farley]

Bear in mind that the Amprobe is reading in ppt sodium chloride. You'll have to convert that to ppt seawater as they are not the same.

For example, 32.9 ppt (33.64 g/L) NaCl has the same conductivity as 35 ppt seawater.

I discuss that here:

Reef Aquarium Salinity: Homemade Calibration Standards
http://reefkeeping.com/issues/2004-06/rhf/index.htm

 

[rwb500]

thanks randy! I calibrated it with the pinpoint calibration fluid. does that mean it is OK? in the future i was planning on using your calibration fluid recipe. that will work, right?

edit - also thanks to jcw for sharing that info about the Pinpoint. I didnt know that. Maybe I would have bought a digital refractometer if I knew about these downfalls.

 

[Randy Holmes-Farley]

If you calibrated it with the pinpoint fluid and set it to read 35 ppt, then yes it is good to go for most reef applications except hyposalinity, which is actually closer to the 0 ppt than 35 ppt and is better served by using RO/DI calibration.

The Pinpoint does take a bit longer than my Orion to stabilize. In all cases, I think that is because the device needs to measure temperature accurately to get the salinity, and so it takes a bit of time for the probe to come to tank temp.