nothing matches up.

[FraggledRock]

So i have and compare A Refractometer and 2 different brand hydrometers.

I am starting to believe the only reliable source is my Instant Ocean Hydrometer.

There are my readings

Refractomter - 1.020 SG
Fluval Hydrometer 1.023 SG
Instant Ocean Hydrometer - 1.026 SG

the reason i believe my IO hydro is most accurate is:

calcium is 500 ppm
Alk is 12 dkh
magnesium is 1350 ppm
temp 77.6 F

for this to be right, which i test with ELOS tests, my salinity would have to be matching the highest salinity reading with brand new RODI water and red sea coral pro salt, right?

[delor-02]

Does your refractometer adjust for temp? Might want to check it against a calibration standard.

[FraggledRock]

Originally Posted by delor

Does your refractometer adjust for temp? Might want to check it against a calibration standard.

it one of those ATC Auto Temp Compensation refractometers from amazon.

how well it compensates I dunno...

[LeRenard]

My IO hydrometer is off by about +.006.. you'd have a hard time convincing me your refractometer is wrong and the IO hydrometer is right.

[delor-02]

Originally Posted by LeRenard

My IO hydrometer is off by about +.006.. you'd have a hard time convincing me your refractometer is wrong and the IO hydrometer is right.

I agree. I'd believe the refracometer before a swing arm hydrometer.

[gone fishin]

Have you calibrated the refractometer? If you have confidence in the calibration then I would believe it.

[FraggledRock]

Originally Posted by gone fishin

Have you calibrated the refractometer? If you have confidence in the calibration then I would believe it.

I never calibrated it.

I am actually not too keen on how to calibrate it.

I kinda just opened it and started using it LOL

[gone fishin]

They typically need periodic calibration. Most are calibrated with a 1.026 solution. I believe you can get some from BRS or someplace like that. there is usually a set screw used to adjust the refractometer.

[FraggledRock]

Originally Posted by gone fishin

They typically need periodic calibration. Most are calibrated with a 1.026 solution. I believe you can get some from BRS or someplace like that.

I just calibrated it with fresh RODI water to 0 using the adjustment screw

now it read 1.023 like my fluval.

is it bad to calibrate with RODI to 0?

[supervdl]

you have to calibrate these things otherwise you will be creating a disaster one of these days. Hydrometer I don't trust at all. I also found over the years if I keep the refractometer at a room with a different temperature and move it around a lot it has to be calibrated more often. Not sure if this is true but that's my observation.

[gone fishin]

It may be off still. When we do a one point calibration we like to use the point that we are looking for, in this case 1.026. That being said there are a couple refractometers out there that the directions call for DI water but follow your directions that you got with the unit.

[FraggledRock]

Originally Posted by supervdl

you have to calibrate these things otherwise you will be creating a disaster one of these days. Hydrometer I don't trust at all. I also found over the years if I keep the refractometer at a room with a different temperature and move it around a lot it has to be calibrated more often. Not sure if this is true but that's my observation.

I keep mine in my tank stand ;P

[FraggledRock]

Originally Posted by gone fishin

It may be off still. When we do a one point calibration we like to use the point that we are looking for, in this case 1.026. That being said there are a couple refractometers out there that the directions call for DI water but follow your directions that you got with the unit.

it didnt come with any =/

[gone fishin]

LOL that sucks. I would not really trust it until I could calibrate it with a 1.026 solution. The DI may be spot on or it could be off a few points.

[FraggledRock]

Originally Posted by gone fishin

LOL that sucks. I would not really trust it until I could calibrate it with a 1.026 solution. The DI may be spot on or it could be off a few points.

tell me about it!

there's always an obstacle. lol

since with the RODI i am using I am in between the original reading, my highest reading of 1.026 and my mid reading of 1.023.

i think it is safe to say i am not THAT far from 1.025 lol

can 1.024 be that lethal to a reef tank?

this is a salinity refractometer, so thre is less chance of error using rodi?

i read that even the calibration fluids can be problematic....

[FraggledRock]

mine looks exactly like this:
http://www.glassreef.com/review_d-d_refractometer.php

but mine goes to 1.000 and 0 ppt

[gone fishin]

1.024 will not cause any long term effect. Corals may get a little grumpy.

[FraggledRock]

Originally Posted by gone fishin

1.024 will not cause any long term effect. Corals may get a little grumpy.

no coral yet. restarted from tank crash last week =/

just trying to get my head around all the possible future downfalls i was overlooking/wasnt aware of prior....

[gone fishin]

Yeah forgot about the restart. I don't think you would have any issues.

[FraggledRock]

Originally Posted by gone fishin

Yeah forgot about the restart. I don't think you would have any issues.

cool =)

thanks for the help!

[kmbyrnes]

My refractometer looks almost exactly the same. Got it from BRS. It came with 35 ppt calibration solution.
There are threads here that discuss WHY you want to calibrate to that and not zero.
They boil down to the fact that these hobby grade devices are not super accurate across the entire scale, so it would be best to be accurate at the point you want to measure.
With mine calibrated to 35 ppt, RO/DI reads less than zero and when I calibrate to zero with RO/DI, the calibration solution reads about 31 ppt.
In your case, I would NOT trust the refractometer until it is properly calibrated.


http://www.bulkreefsupply.com/aqua-c...ion-fluid.html

.

[dkeller_nc]

FraggledRock - Yes, you must calibrate a refractometer with a solution specifically made for calibrating refractometers to read properly in seawater. Bulk Reef Supply sells a bottle for $6, and so do quite a few other retailers.

Others have already noted this on the thread, but I also wanted to point out that you may have a refractometer that's intended for reading brine solutions (i.e., solutions of pure NaCl) and not seawater. That's OK, it'll still work for aquarium use, but simply zeroing a brine refractometer with RODI means it'll be off in seawater by about 0.003.

If you'd like full details, this article will give you a lot of information.

[FraggledRock]

Thanks for the info!