Hydrometers vs Salinity Pen

[Hugh Mann]

So, I've been trying to nail down the salinity in my tank, I bought two hydrometers, a Fluval one with a suction cup to keep in the tank, and an Instant Ocean to double check and measure new water.

As it sits right now, I mix 1lb 6.4oz of Instant Ocean Reef Crystals into 5 gallons of RO water, which at a temperature of 75f gives the Fluval a reading of 1.0215, the Instant Ocean reads 1.0225, an agreement within the error bars of both hydrometers (+/-0.001). For reference, the bucket of salt lists 1.4lbs of salt should equal 1.021 in 5 gallons of water.

Now, a friend of mine brings over a Posidon Salinity Pen, a $200 instrument against my two $12 hydrometers, and it reads 1.019, and he had properly calibrated it.

What's going on here, which reading should I trust? If the pen is wrong and I follow it, I'll have way too much salt, and if it's right, and I don't, not enough salt.
Hoping someone can help me out with this. Thanks!

 

[Cell]

The correct answer is buy a refractometer. But trust the pen over the hydrometer. Refractometers are only about $20.

 

[Johniejumbo]

Good question. I’ll follow along for info sake.
what temp is the pen calibrated to? And is the water 75 degrees? If so.1lb is a lot less than 1.4lb and the salt levels you listed aren’t that much different. I mean per the instructions you said 1.4 should be 1.021 at 75 degrees and you say 1lb is 1.0215 ish. If all info is being considered your salt may be lower than the float tests say. Which sucks because I use that instant ocean hydrometer!

We need answers!

 

[GoVols]

I would not use an hydrometer for a coral reef.

The Vee Gee STX-3 is the best refratometer that I've ever owned.

Sometimes it pops up on sale for $80

Always calibrate with .35 solution with any refractometer.

The reviews don't to look good, on that pen

 

[Hugh Mann]

The correct answer is buy a refractometer. But trust the pen over the hydrometer. Refractometers are only about $20.

I did buy one, and promptly returned it as it's calibration was constantly drifting, gave different readings on the same sample, usually reading in the 1.030-1.035 range. Admittedly it was a cheap one, but I can't afford to drop $200 on an expensive one at the moment.

 

[Hugh Mann]

I would not use an hydrometer for a coral reef.

The Vee Gee STX-3 is the best refratometer that I've ever owned.


Sometimes it pops up on sale for $80

Always calibrate with .35 solution with any refractometer.

The reviews don't to look good, on that pen

I don't actually have a reef, fish only, and it's going to stay fish only. I know fish only gives me a larger room for error, but I would prefer to have it at a steady 1.023.
I'll keep an eye on that one. Thanks.

 

[GoVols]

I don't actually have a reef, fish only, and it's going to stay fish only. I know fish only gives me a larger room for error, but I would prefer to have it at a steady 1.023.
I'll keep an eye on that one. Thanks.

Yeah,
An hydrometer will do the job for ya

Mix some new salt and take to your local reef shop:
Have your local reef shop test on they're meter, then use a sharpie to mark your hydrometer at their shop...

 

[Jeremy Luke]

I've never had drifting from my refractometer. I bought it for $35. I do occasionally have to recalibrate it. It's a solid tool.

 

[rusty hannon]

So, I've been trying to nail down the salinity in my tank, I bought two hydrometers, a Fluval one with a suction cup to keep in the tank, and an Instant Ocean to double check and measure new water.

As it sits right now, I mix 1lb 6.4oz of Instant Ocean Reef Crystals into 5 gallons of RO water, which at a temperature of 75f gives the Fluval a reading of 1.0215, the Instant Ocean reads 1.0225, an agreement within the error bars of both hydrometers (+/-0.001). For reference, the bucket of salt lists 1.4lbs of salt should equal 1.021 in 5 gallons of water.

Now, a friend of mine brings over a Posidon Salinity Pen, a $200 instrument against my two $12 hydrometers, and it reads 1.019, and he had properly calibrated it.

What's going on here, which reading should I trust? If the pen is wrong and I follow it, I'll have way too much salt, and if it's right, and I don't, not enough salt.
Hoping someone can help me out with this. Thanks!

Was thinking about going all digital after buying a digital ph meter and am very curious hw this works out for you. Best of luck in your quest and hope it doesn't cause any serious problem s will be watching to see how it goes n sorry I have no useful info R

 

[Hugh Mann]

I've never had drifting from my refractometer. I bought it for $35. I do occasionally have to recalibrate it. It's a solid tool.

Which one did you buy? That's about what I paid for mine, and it was better suited for hammering nails than measuring salinity.

 

[Hugh Mann]

Yeah,
An hydrometer will do the job for ya

Mix some new salt and take to your local reef shop:
Have your local reef shop test on they're meter, then use a sharpie to mark your hydrometer at their shop...

I might just do that, though my "local" shop is about a 9 hour round trip with traffic.

 

[Hugh Mann]

Good question. I’ll follow along for info sake.
what temp is the pen calibrated to? And is the water 75 degrees? If so.1lb is a lot less than 1.4lb and the salt levels you listed aren’t that much different. I mean per the instructions you said 1.4 should be 1.021 at 75 degrees and you say 1lb is 1.0215 ish. If all info is being considered your salt may be lower than the float tests say. Which sucks because I use that instant ocean hydrometer!

We need answers!

He tells me it automatically compensates for temperature, but I don't know what temp it was calibrated at.

My results testing the Instant Ocean at home have been thus. 61 is my typical room temp, 75 is my tank temp.
1lb4oz=1.019@61f
1lb4oz=1.020@75f

1lb6.4oz= 1.021@61f
1lb6.4oz= 1.022@75f

1lb8oz= 1.025@75f
1lb8oz= 1.023@61f

 

[Jeremy Luke]

Which one did you buy? That's about what I paid for mine, and it was better suited for hammering nails than measuring salinity.

Ok, I just looked. I actually paid $39.99 and I bought it from bulk reef supply.

The one I have is now sold for $34.99 from BRS.

Refractometer for Reading Salinity with Calibration Fluid

Take Control of Your Aquarium's Salinity Level Accurate Readings: Measures salinity from 1.000 to 1.070 specific gravity. Automatic Temperature Compensation (ATC): Provides reliable readings under varying temperatures. Easy Calibration: Maintain accuracy with a quick calibration process...

www.bulkreefsupply.com

 

[Hugh Mann]

Ok, I just looked. I actually paid $39.99 and I bought it from bulk reef supply.

The one I have is now sold for $34.99 from BRS.

Refractometer for Reading Salinity with Calibration Fluid

Take Control of Your Aquarium's Salinity Level Accurate Readings: Measures salinity from 1.000 to 1.070 specific gravity. Automatic Temperature Compensation (ATC): Provides reliable readings under varying temperatures. Easy Calibration: Maintain accuracy with a quick calibration process...

www.bulkreefsupply.com

That looks identical to the one I bought off Amazon, minus the Bulk Reef Supply on it. Might have to give that one a shot and see what it says. Thanks.

 

[Jeremy Luke]

That looks identical to the one I bought off Amazon, minus the Bulk Reef Supply on it. Might have to give that one a shot and see what it says. Thanks.

It's been rock solid for me. Just use an above head light source and move it from down to up until it is extremely obvious where the line is. It will be extremely obvious.

 

[Dugless]

Hydrometers get a bad rap, but they can be useful if you confirm their accuracy with a refractometer. They shouldn’t drift at all if used properly.

 

[mike550]

I completely respect good refractometers but I use a Hanna Salinity Tester myself. Two reasons for my choice. First, I like the digital readout over trying to read the measurement screen. Second. it also measures temperature so I get a second spot check on temp as well.

Either way, calibration is key to accurate readings. I measure salinity 10-15 times per month and calibrate every 30 days which is the suggested schedule from Hanna

 

[Cell]

Actually, if you want to spend a little money, I'd buy the Milwaukee MA871 Digital Refractometer.

 

[Hugh Mann]

Good news everyone!
Turns out that salinity pen went out of calibration. Brought it over today and it was within a half point of my Instant Ocean, and a full point on the Fluval. Well within all acceptable error bars!