RKL Module?? Salinity or ORP, which test is more useful?

Salinity probes are expensive, and often times, inaccurate. I would not trust the life of my tank with one. It is OK as a spot check / glance at screen reading, and perhaps an e-mail alert, but there is no way I would put much trust in a conductivity probe.

ORP is a good way of telling water quality. The higher the ORP, the better, up to an extent. Steve's description above is excellent.

 

I certainly would go for ORP which Steve has explained meaningfully. Apart from that, we can consider on normal tank condtions and to evaluate whisch tends to varied more frequent and usually needed the aid through electronic device other than experienced observation and careful setup considerations. ORP can be changed under many situations in short period while salinity is not that difficult to control and controlled. Not to mention if O3 is in use.

 

The expansion card for my Profilux 2 will alloow measurement of both salinity and Redox. I bought a salinity probe but didn't bother getting a Redox probe. As near as I can tell, making management decisions based on the redox potential in your tank is fuzzy at best. Redox varies a great deal during the course of a normal day and definately varies every time you do a water change. There are a lot of things that we measure in our tanks where it is well established what the desirable ranges are (salinity, alkalinity, calcium, tempreature) but the 'science' behind what redox levels are most beneficial to a tank has yet to be developed.

 

This is what I've read as well, well put.

 

I pulled the trigger and got a Reef Keeper Lite level 3.. I cant wait..

Thanks for all the help..

 

ORP has a huge acceptable range, and unless you are using ozone, it won't get out of those levels.

That is why I consider it a meaningless thing to monitor.

 

this shouldnt even be a discussion if these probes arent accurate. If someone doesnt trust a hydrometer, why should you trust a probe? Ive never used one so i dont know but i hear they are very innacurate. If thats the case, ORP for sure. This might not have helped much, but it gives you a different angle on things

 

Cira-- just to present the another angle on this subject, here is note from the guy who owns aqua-digital in Ottowa. In the interest of full disclosure, he is the North American Distributor for Profilux but here is what he had to say about (his) salinity probes...

We recently completed a case study testing various brand refractometers against electronic conductivity devises, including ProfiLux.

The findings were very interesting and I thought I would sahre this with you as so many users question why does the $300 probe of profiLux read less than my bargian refractometer. Well here is the REAL answer!

The first test was as follows.

calibrate 3 devises per manufacturers guidelines

Refractometer
Digital salinity pen
Digital conductivity monitor
PROFILUX SALINITY PROBE ON A PROFILUX PLUS II EX

The next step was to do a test using only the guidelines of each devise.

The refractometers read using GHL calibration solution around 1.018ssg

All other devises read 1.024ssg

We then swapped the calibration fluid fluid with another brand and the readings did not change as expected.

Next step was to make sure all devises other than the Auto temperature compensated (built in feature) refractometers were at the same temperature of 22oC ALL units stayed the same other than the refractometer which reading crept up to 1.020ssg.

At this point I had already worked out that the temperature compensation of refractometers was not really doing its job on all ones tested so passed the evaluation to Brent of Big Al's in Montreal Canada.

Here is his findings. (copied text from email)

The digital units seem to work really well, and really doesn't agree very well with the refractometer. The digital pens are consistent with our conductivity meter, and the conductivity measurement on the Profilux, and consistent with various salinity calibration solutions that we have. That it agrees with the conductivity meter is not surprising to me, as it is also, well, a conductivity meter.

All this tells my pea-sized chemical engineer mind is that conductivity meters, calibrated using a standard solution (which may or may not contain all the minor 'noise' level ions such as Mg, Ca, etc), provide consistent conductivity measurements of saltwater solutions... From a technical standpoint, given the dominant nature of the Na and Cl ions in saltwater, conductivity should translate very well to salinity. And temperature compensates very easily. Yet the basic engineering behind a refractometer is also solid. Although refractive index (as a proxy for density as a proxy for salinity) is temperature dependent, it is not strongly so (heat water in a pot on your stove from 25 Celsius to 75 Celsius, and the water level does not change significantly). And it does not account for the difference in measurement that you found in your testing a week or two ago.

All of which brings to rise a few questions:

•How strong (or poor) is the temperature compensation on refractometers?
•Given that the heat capacity of a drop of water is MUCH less than the heat capacity of the prizm on the refractometer, do we need to heat a refractometer up to the exact temperature of the solution we are measuring in order to get a proper reading?

This is the point we are all missing, in my humble opinion. It is practically inconsequential what the temperature of the drop of water was prior to the application on the refractometer; it is only important the temperature of the solution on the glass. And the glass temperature has a huge impact on that measurement.

I am coming around to the fact that conductivity is a better proxy for salinity than is refractive index, at least within the context of the marine aquarium hobby.

Back to me -

To sum up - irrelevant of your refractometer stating it has ATC (auto temp compensation) if you want an accurate reading with a refractometer make sure the glass is the same temp as the testing solution, but as this is quite impossible then better still buy the accurate Profilux salinity probe and get true readings every time!

Class dissmissed


Please note that I'm not trying to advance a particular agenda here or to promote any particular product. I just thought that there might be 1 or 2 folks who would be interested to see this. Happy Reefing, GTS.

 

Cira, I see you point, but when you look at ORP a little more in depth, you will find out that monitoring that too is a waste of $$, perhaps even more if you don't use ozone.

I say monitor neither ORP or salinity and buy another fish or something.

 

Or more coral.. Not to mention I just spent $300 on new corals and none of you people commented on my build.. Boo