Tropic Marin HIGH PRECISION HYDROMETER, claim's it's super accurate and never needs calibrated.

[kenchilada]

I also enjoy their precision thermometer.

I didn’t know about the thermometer!

 

[X-37B]

I didn’t know about the thermometer!

I prefer the old mercury ones.
I have one thats over 35 years old.
You can still find them on ebay.
I will have to look up the TM one.

 

[Reef.]

I also enjoy their precision thermometer.

Just thought I'd summarize a few points.

No it doesn't require calibration but do test with a standard when you get it...
The TM floating hydrometers is calibrated when manufactured. It is unusual but possible to receive one that was not calibrated properly which could determined by putting it in a standard. If it's off, you now know by how much and can use it accurately. it is also unlikely but possible for the printed paper inside to shift which I suppose you could also measure using a standard too lol. The takeaway here is compare it to a standard first thing.

Yes you need to compensate for temperature...
These are great for measuring salinity in our tanks near 77 degrees (temperature the hydrometer was calibrated to when made). For best accuracy use a chart but at temp of 78 or 79 I wouldn't even bother adjusting, just remember that as temperature increases the actual salinity becomes slightly higher than the reading. If you are at 80F add roughly 0.0006. If you want to use it to measure newly made saltwater which has not been warmed, there will be significant temp compensation, then definitely use the chart from Randy Farley's old article or an online calculator. If you're primarily looking to test the salinity of newly made cool saltwater then maybe a digital refractometer that compensates for temperature would just be easier.

Read at plane of water...
Read the value at the plane of the water and not the meniscus. Said another way, the water is slightly raised around the hydrometer (the meniscus), do not read it there, read at height of most of the water.

Keep it clean...
Rinse with rodi to keep it free of salt buildup, use citric acid or something if there are deposits.

This thing is pretty great

An article further explaining this: http://www.reefkeeping.com/issues/2004-07/rhf/#a
To make the standard: http://www.reefkeeping.com/issues/2004-06/rhf/index.php

Thanks for that info.

I’ve just ordered one, think I’ll probably carry on using the refractometer when making salt water as my water is normally quite cold, I’ll check what the reading should be and if it’s not a silly number ie between two lines then I’ll use it when the water is colder too, I’ll also use the hydrometer when I heat the water just before adding for a final check and also use it for the tank.

Just hope it arrives in one piece now.

 

[xxkenny90xx]

I have an old one from the 90s. It's the most accurate salinity measuring tool I have. But don't permanently leave it in the sump as some have suggested. Algae will grow on it and weigh it down (therefore changing your readings)

 

[Midrats]

Thanks for that info.

I’ve just ordered one, think I’ll probably carry on using the refractometer when making salt water as my water is normally quite cold, I’ll check what the reading should be and if it’s not a silly number ie between two lines then I’ll use it when the water is colder too, I’ll also use the hydrometer when I heat the water just before adding for a final check and also use it for the tank.

Just hope it arrives in one piece now.

It comes in a rugged three piece plastic sleeve, it'll arrive intact.

 

[Reef.]

It comes in a rugged three piece plastic sleeve, it'll arrive intact.

That’s reassuring., I’ll hold you to that

Shame they didn’t stock the measuring cylinder but I guess I don’t really need it, would have been nice to get though.

 

[Saltyreef]

the tropic Marin is 25c.

Yes, because its designed for reef aquariums

 

[Reef.]

Yes, because its designed for reef aquariums

Yeah I realise that, was just saying it was 25c as apposed to the 60f you said the standard hydrometer are calibrated at.

 

[salty joe]

I have a TM hydrometer, it's the only thing I trust 100%. I can't get a good look at it in the tank, so I made a cylinder of 2" acrylic pipe. I use it to make sure my refractometer is true every month or so.
Calibration fluid for refractometers goes bad, the hydrometer is so much better, I love it. I really like that it has a large scale and that it it measures a tight range.

It's important to spin the hydrometer to remove tiny bubbles that can get caught on the surface.

 

[Snoopy 67]

When I had mine I used the plastic cylinder it came in to test a sample.

 

[Reef.]

When I had mine I used the plastic cylinder it came in to test a sample.

that’s good if the tube it comes in and be used for that.

 

[Saltyreef]

Yeah I realise that, was just saying it was 25c as apposed to the 60f you said the standard hydrometer are calibrated at.

60 degrees is a US standard for specific gravity hydrometers.
You can buy a standard hydrometer calibrated at 60 degrees with the same scale give or take some resolution.

The only reason this is calibrated to 77 degrees is it is a specialty hydrometer.
Not standard.

 

[Saltyreef]

When I had mine I used the plastic cylinder it came in to test a sample.

Yep. Since it will be big enough

This is what i do with the ones at work too when i cant float them in a brine tank full of salt.

Bur someone got cute and bought a glass graduated cylinder. It wont last long >.<

 

[Reefinmike]

I got brs to start carrying these hydrometers. I've confirmed the accuracy beyond any doubt using @Randy Holmes-Farley's calibration solution weighing everything with great precision. I have Two myself and have compared them against two other TM hydros... they're all identical. Best $31 you'll ever spend

 

[MentalNote]

Thanks all for this thread! It convinced me to buy a TM Hydrometer back in November.

I learned that my refractometer was off, and that BOTH my calibration solutions were wrong too. After adjusting salinity to ~1.0255 (to account for hydrometer possible deviation of up to .001), I must say my tank is solid.

My LPS were instantly happier. This includes a bubble coral that had slowly receded over the years. I even find using the hydrometer is easier then the refractometer. Or maybe I think its just more fun and science-y... use the beaker... spin the hydrometer slightly as it gets a reading.....watch it bob and then settle out.

Anywho, thanks! Cheapest solution in a long time.

 

[salty joe]

Yeah, the fact that I had calibration fluid that went bad over time is what convinced me to get this hydrometer.
No regrets. I can hardly believe it cost so little.

 

[Reef.]

Yeah, the fact that I had calibration fluid that went bad over time is what convinced me to get this hydrometer.
No regrets. I can hardly believe it cost so little.

Yeah handmade too.

Getting mine today or tomorrow hopefully, just coming in time as I have just tested my mag and cal, both are higher than they should be, all I can think of is my salinity may be off, this should settle that question.

 

[acabgd]

I've had one for years, it's now at my LFS and I use it as and when needed. Just to show the precision, here is a photo of what it looks like. You can virtually read 1.0250, 1.0251, 1.0252...

You also get an idea of scale, this thing is big, the tip is almost 13cm long, so about 5" plus the bottom part which is even longer.

TM did use to have an even more precise hydrometer with 0.0005 resolution back in the day - or so they claimed



Note it goes up to 1.028 (if you're worried about that)

 

[Adamantium]

I wonder why they put the “green zone” between 1.022 and 1.024....

 

[Reefinmike]

I wonder why they put the “green zone” between 1.022 and 1.024....

that's actually a density model; slightly different than specific gravity