salinity measures: swing arm/floating hydrometer, refrac, electrical conductance

CTaylor · 06/09/2018, 01:03 PM

All three are indirect measures of sailinty, when we are trying to estimate actual amount of salt in the tank, as in ppt (35 being the target usually). And all salt mixes are different from each other. Probably even batches of the same brand have variances in the proportions of each ion etc between batches. Hydrometers measures how bouyant something is in the salt water mix, refracts measure how the light bends,conductance measures the electrical properties of the water mix. But none can tell you exactly the amount of salt overall. Say for example you more iron in the mix, and less Mg, but still the same overall weight, then you'll have different readings on each of the measuring methods above. This is b/c Mg might cause different buoyancy and refraction and electrical conductance than Iron, and vice versa. But both mixes have the same salt content.

You can't really rely on store bought standards because their mix of salt is not what your mix of salt it.

Also I was wondering why people rely more on refracts than swing arm hydrometers. Or where testers like the icecap tester (electrical) fall into how close it is to estimating true density of salt in mine or your specific tank. Which of the three in reality is the best general use to most closely estimate how much salt is actually in the tank? I'm thinking the only way is to have your specfic salt water mix analyzed to find the exact proportions of all the elements etc in the water, figuring out the salinty of your specific tank, and using that as your standard, calibrating whatever you use to measure to that standard.

I used to think salinity was the easiest thing to measure and know for sure if you're off target or not, but thinking about it, it's just not the case I dont think.

billdogg · 06/09/2018, 02:32 PM

I have had a pair of swing arm hydrometers for 30 years, and they still read exactly the same today as they did then. About 5 years ago I succumbed to peer pressure (TYVM RC!) and bought a refractometer. After calibrating it per specifications, I found that one of my hydrometers was read about .002 low, the other about .001 high. I marked them accordingly and use them to this day. They are just too simple to set aside due to a minor error. I use the refractometer maybe once every couple months just to say I did, but IMHO, either will work just fine. Like everything else in this hobby, stability is the key, not some magical number that must be spot on to avoid killing everything in your tank.

Pick a tool (or two), test them so you know where they test at, and then use them. And stop obsessing! Lord knows there is plenty of other things to obsess about>

CTaylor · 06/09/2018, 02:38 PM

it's attention to detail

. and it makes if youre using something to measure something to know that your result is near what it actually is.
And right, precision is one thing, but accuracy was also what I'm looking for also.

mcgyvr · 06/09/2018, 05:58 PM

Quote:

Originally Posted by CTaylor

it's attention to detail

. and it makes if youre using something to measure something to know that your result is near what it actually is.
And right, precision is one thing, but accuracy was also what I'm looking for also.

Oh the irony..
"Attention to detail" yet can't form a complete sentence right after that without mistakes..

CTaylor · 06/09/2018, 07:55 PM

Probably the best way to make your own mix of salt based on salt weight and water weight (red sea supposedly has 5 grams of water per 35 grams of salt). And just whatever way to measure you like based on that as the calibration. PIA, but I think salinity should be within 10% of what the corals and fish normally live in.

06/09/2018, 01:03 PM	#1
CTaylor Registered Member Join Date: Nov 2001 Posts: 1,524	salinity measures: swing arm/floating hydrometer, refrac, electrical conductance All three are indirect measures of sailinty, when we are trying to estimate actual amount of salt in the tank, as in ppt (35 being the target usually). And all salt mixes are different from each other. Probably even batches of the same brand have variances in the proportions of each ion etc between batches. Hydrometers measures how bouyant something is in the salt water mix, refracts measure how the light bends,conductance measures the electrical properties of the water mix. But none can tell you exactly the amount of salt overall. Say for example you more iron in the mix, and less Mg, but still the same overall weight, then you'll have different readings on each of the measuring methods above. This is b/c Mg might cause different buoyancy and refraction and electrical conductance than Iron, and vice versa. But both mixes have the same salt content. You can't really rely on store bought standards because their mix of salt is not what your mix of salt it. Also I was wondering why people rely more on refracts than swing arm hydrometers. Or where testers like the icecap tester (electrical) fall into how close it is to estimating true density of salt in mine or your specific tank. Which of the three in reality is the best general use to most closely estimate how much salt is actually in the tank? I'm thinking the only way is to have your specfic salt water mix analyzed to find the exact proportions of all the elements etc in the water, figuring out the salinty of your specific tank, and using that as your standard, calibrating whatever you use to measure to that standard. I used to think salinity was the easiest thing to measure and know for sure if you're off target or not, but thinking about it, it's just not the case I dont think.

06/09/2018, 02:32 PM	#2
billdogg Registered Member Join Date: Apr 2008 Location: Grove City, Ohio Posts: 10,806	I have had a pair of swing arm hydrometers for 30 years, and they still read exactly the same today as they did then. About 5 years ago I succumbed to peer pressure (TYVM RC!) and bought a refractometer. After calibrating it per specifications, I found that one of my hydrometers was read about .002 low, the other about .001 high. I marked them accordingly and use them to this day. They are just too simple to set aside due to a minor error. I use the refractometer maybe once every couple months just to say I did, but IMHO, either will work just fine. Like everything else in this hobby, stability is the key, not some magical number that must be spot on to avoid killing everything in your tank. Pick a tool (or two), test them so you know where they test at, and then use them. And stop obsessing! Lord knows there is plenty of other things to obsess about> __________________ I'll try to be nice if you try to be smarter! I can't help that I grow older, but you can't make me grow up! Current Tank Info: 120 mixed reef with 40b sump, RO 150 skimmer, AI Sol Blue x 2, and a 60g Frag Tank with 100g rubbermaid sump. 2 x Kessil A360w lights, BM curve 5 skimmer

06/09/2018, 07:55 PM	#5
CTaylor Registered Member Join Date: Nov 2001 Posts: 1,524	Probably the best way to make your own mix of salt based on salt weight and water weight (red sea supposedly has 5 grams of water per 35 grams of salt). And just whatever way to measure you like based on that as the calibration. PIA, but I think salinity should be within 10% of what the corals and fish normally live in. Last edited by CTaylor; 06/09/2018 at 08:08 PM.

06/09/2018, 02:38 PM	#3
CTaylor Registered Member Join Date: Nov 2001 Posts: 1,524	it's attention to detail . and it makes if youre using something to measure something to know that your result is near what it actually is. And right, precision is one thing, but accuracy was also what I'm looking for also.