Swing Arm Hydrometer Warning!

[Pghjeff71]

Ever since I've been in this hobby I've always used a swing arm hydrometer of one type or the other. I've been using the "Deep Six" model for the last several months and while being here on the AA forums have read nothing but bad things about these. I've always thought, "well how bad can these things truly be". Well after a disease outbreak and needing to use hyposalinity for a quarantine tank I decided to purchase a refractometer. The difference between the two devices is staggering.

- The swing arm hydrometer is off by a whopping -.5/SG; for example the refractometer showed my main tank at 1.26SG while the hydrometer showed 1.21SG.

Let this be a warning to everyone in this hobby. Spend the $45 dollars and get a refractometer today! It's the single best tool you can buy if you are serious about the care of your tanks.

 

[Pghjeff71]

Oh as a sidenote, while I was typing this article I remembered I also have a glass hydrometer (the kind you drop in the water and see where it floats). I've had this thing probably for a good five years now, and this one is +.2SG as compared to the refractometer:

Main Tank:

1.23SG (refractometer)
1.25SG (glass hydrometer)
1.18SG (swing arm hydrometer)

Not as bad as the swing arm hydrometer, but still leaves room for doubt.

- Jeff

 

[Scatcat]

Thank you for sharing, this is one of the reasons why I read these post everyday. I use a refractometer and I'm glad I spent the money. As much as I stress about my tank I want to make sure all readings are accurate.

 

[Kam]

I also just recently changed from a hydrometer to a refractometer. I had similar results, a .5 difference between the two. My refractometer readings match that of the LFS that uses some kind of digital meter.

 

[Jermz79]

Same here ... I was using an "Instant Ocean" hydrometer and it was giving me a reading of 1.028 ... I decided to go ahead and get myself a refractometer (the blue one from premiumaquatics.com) and when I got it my readings were 1.024!

A BIG DIFFERENCE!!!!


Needless to say the hydrometer went in the garage!!!

 

[Phyl]

That's so funny. I've noticed exactly the opposite. Most of my fellow reefers that think they have their tanks running at 1.025 using a swing arm actually have their water at 1.029 using the refractometer. Wrong in any direction is just wrong, but I find it interesting that it is wrong in both directions.

 

[revhtree]

My Refrac says 1.025 my Instant ocean Hydro says 1.025..

 

[dianeww]

I'm going with you, revtree....lots of conflicting advice here. If I stick with my floating arm hydrometer and just keep the level consistent (mine reads 1.023, and that's what I adjust the new water to too), that can't be too far off the mark.

 

[dianeww]

Sorry about the misspelling, revhtree!

 

[Phyl]

As the salt deposits over time they will become increasingly inaccurate. I'd double check it every month at the LFS, just to be sure it hasn't changed any.

 

[revhtree]

Thats true. I think my hydro is about 1yr old.

 

[ellisz]

My Deepsix was off at 6 months. I thought I was at 1.025 and I was really at 1.029! Everthing seemed fine but it took a long adjustment to get it down. I marked my Deepsix with the correct reading I still use it now

Sometimes the swing arm is quicker in a pinch. Just calibrate it with the refractometer on occasion.

 

[dianeww]

If you give the swing-arm type a good soaking in plain water from time to time will it keep the salt deposits from forming?

 

[maxamillion]

your probably better off leaving freshwater in it while you store it, then when you are ready to use it then dump that out and do your tests and then fill it back up with fresh water. This way the salt and any other minerals in the salt water and or freshwater that you should rinse it out with after you test, doesn't dry up on the swing arm, thus causing it to be so innacurate.

 

[saltwatersmac]

I've checked my Deep Six hydrometer against a refractometer.

Hydrometer => 1.021
Refractometer => 1.024

The hydrometer seems to be consistently off by .003 on the low side. I just try to keep it reading around 1.021 and it works for me as long as its consistent. I rinse the hydrometer off in RO water after every use. This keeps the deposits off.

Stephen