Refractometer constant recalibration

[eugreef]

I got the marine depot refractometer. I habitually calibrate my refractometer every time I use it. I just got it about 2 weeks ago brand new so ive been checking to see how long it holds calibration. I read the calibration articles by Randy Holmes-Farley. The ones about making your own solution and how to calibrate accordingly. I have to my disposal a very high precision gram scale so I know that my standard is 35ppt. To be sure I bought a 35ppt refractometer calibration solution made by aqua craft. They do match up so I know they are both accurate to 35ppt. Here is my dilema: whenever I check to see if my refractometer is calibrated it is always, ALWAYS off by about +5ppt, when rechecking at 24 hour intervals. The refractometer is repeatable when I check it within 30 min of calibrating. I dont know when it starts to loose its accuracy. Is it normal that I am having to constantly recalibrate?

Im thinking that it might have something to due with the room temperature, but the marine depot refractometer is auto temp correcting. So i dont know. anyone?

[Shane Hoffman]

I only calibrate mine a few times a year....and ususally its only off 1 or 2 ppt

[DThompson]

The calibration could be off from a difference in temperature. I calibrate before every use. I believe the swings in calibration can be greater in the winter. Not sure if that is your problem, but that would be my first guess.

[krowleey]

i have had the same problems with my MD refracto. I think they are just junk.

[NanoReefWanabe]

i only ever do mine once or twice a year...never off by too much... i think i wold have shot myself having to recalibrate every use...

[Rybren]

I have a similar issue with mine. My directions indicate that it should be recalibrated if the unit is exposed to a 5 degree F change in temp.

The ambient temp where my tank and refractrometer are is about 68 degrees in the winter. Just holding the unit for any length of time will cause a temp swing of more than 5 degrees. Once I've finished with it and it's put away, the temp of the unit will drop, sending the calibration off.

Perhaps those folks who don't any trouble with theirs are storing the unit at higher temps, lessening the swing.

[brenndm]

changes in temp will cause this

[clittrell]

I had the same issues. I sent the first one back and the second one had the same issues. I sent the second one back and got a "Milwaukee Refractometer with ATC (automatic temperature compensation)" from AC. It was $20 more but totally worth it. So much clearer always stays calibrated. I have had great dealings with MD, they are very helpful they just don't make a good refractometer.



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[MaLi]

Had one before with this "habit". My believe is that was a mechanical malfunction of the ATC mechanism (so to speak). The small screw pushes against a bi-metal lamela and if this is not rigidly mounted on the body it starts moving around and causes jumps up and down of the reticular scale. It usually happens when the refractometers suffers mechanical traumas.
If this is the case, toss it away and buy another one. It is not worth the effort to fix it.

my two cents,
Marian

[Fish4Me2]

I had this same problem, only it was a huge difference after every use, no matter how close together. It was suggested that perhaps the crystal inside it was loose, which would explain the constant shifts, each time I moved it.

I agree with the above - toss or return it and find a new one. I've got one I dropped on the floor, with a crack in the crystal, and it STILL stays calibrated for months!

[MaJaCa]

I got a refractometer that has ATC from ebay for 31.50 including shipping. I've been using it for about 2 months and so far its been spot on. You might want to look into it.

Ebay Refractometer (http://cgi.ebay.com/Salinity-Refractometer-Aquarium-Hydrometer-Refratometro_W0QQitemZ370221709361QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item5632eef831#ht_3018w t_933)

[Randy Holmes-Farley]

I'm a bit confused about exactly what you mean is happening.

One day you calibrate and the standard at room temp reads 35 ppt, and then the next day at the same temp and no adjustment the same standard reads 40 ppt?

That obviously is not a temperature concern, if that is what is happening.

[harper]

I had the same problem with one I bought about 10 years ago. Was using ro/di to calibrate then, but it would shift 3+- ppt each day. Something to do with the ATC. Never could figure out why. Using one from BRS now, though cheep it stays calibrated.

[eugreef]

I'm a bit confused about exactly what you mean is happening.

One day you calibrate and the standard at room temp reads 35 ppt, and then the next day at the same temp and no adjustment the same standard reads 40 ppt?

That obviously is not a temperature concern, if that is what is happening.

When I calibrate with the standard at room temperature I calibrate to 35ppt (as I should).

The next day I check to see if the standard reads 35ppt and it does not, it reads around 38-40ppt.

And this happens very consistently!

[eugreef]

I am very unsatisfied with the marine depot brand refractometer and I plan on returning it. This is the email I just sent them:

To:customercare@marinedepot.com

Marine Depot,

I recently purchased your Marine Depot brand refractometer and have been very unsatisfied with the product. As soon as I opened the product I saw a scratch on the plastic piece that covers the optic. When I flipped the cover over to examine the optic I saw numerous coarse scratches on top of the optic. For the meantime I ignored the scratches and calibrated the refractometer using a 35ppt standard. The next day I used the 35ppt standard to check to see if the refractometer holds calibration and it was off by +5ppt. I did this every day for the last week to verify that the refractometer was consistently inconsistent. Needless to say, I am extremely dissatisfied with my Marine Depot refractometer. The optic was scratched, the plastic lens cover is scratched and the refractometer doesnt even hold calibration for 24 hours. I am going to return this product for a refund and I hope that Marine Depot does not make me pay for shipping.

Order Number: W000XXXXXX
Order Date: 1/11/2010
Product Code: MD2101

I have attached pictures of the scratches for your verification.

Thank You

http://www.sdreefs.com/forums/imagehosting/63404b5ce7c615394.jpg
http://www.sdreefs.com/forums/imagehosting/63404b5ce7d3cd73d.jpg
http://www.sdreefs.com/forums/imagehosting/63404b5ce7d3e5162.jpg

[Lilputian]

This one I found on ebay
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=230359595251&ssPageName=STRK:MEWNX:IT

works flawlessly. I have not had to calibrate it since I got it and it is spot on.

[sfboarders]

My MD refractometer was .020 off when I purchased it. After my cycle I added my CUC and they all died within 15 minutes. I now calibrate my refractometer between every use with calibration fluid because it seems to be off by .001-.003 most of the time.

[Randy Holmes-Farley]

And this happens very consistently!

Sounds like it is broken and requires replacement.

works flawlessly. I have not had to calibrate it since I got it and it is spot on.


How do you check it? It would seem unlikely to come properly calibrated for seawater use.

[eugreef]

And this happens very consistently!

Sounds like it is broken and requires replacement.



Hey Randy,

Can you point me to a couple of different refractometers that you would recommend?

[Randy Holmes-Farley]

I expect the ones from places like Marine Depot are fine, but I don't have specific ones I recommend. :)

[clittrell]

I love mine.

Salinity Refractometer with ATC
by Milwaukee Instruments
TE-MR100ATC


I got it at Aquacave. They price matched D&T aquarium. $64.99.

I never used D&T before so I ordered from Aquacave. The scale is very readable.

Hope it helps.




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[cloak]

OT.

How come you don't see any $5.99 floating glass hydrometers on E bay? The cheap one I have works just fine. Maybe those refractometers are more trouble than their worth.
Why would people be selling them?

;)

[Flipper62]

I have the Sybon FG 100. I calibrate it once a month. I haven't had a problem. I have been using a Refractometer for years.

I also have a Pinpoint Salinity monitor. As long as I calibrate them, they are almost dead on to each other.

[MaLi]

I use a Sybon from Premium Aquatics and though I bought a Pinepoint 35 ppm calibration solution that I use once a month I have touched the screw only once at the beginning. No need so far. Cost me $49.95

Marian

[fasteddie99]

This one I found on ebay
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=230359595251&ssPageName=STRK:MEWNX:IT

works flawlessly. I have not had to calibrate it since I got it and it is spot on.

How do you know if you've never "re"-calibrated it? :frog:

[eugreef]

I returned the marine depot refractometer and got the milwaukee atc100 from custom aquatic. I am a mechanical engineer by profession and I know a good design when I see it. for only 20 dollars more the milwaukee is for superior to the marine depot refractometer.

[d0ughb0y]

I use the marine depot refractometer and only calibrated it once when I first got it.
I still get good reading after like 2 years. I know because when I mix 5 gallons rodi and adding 3 cups salt, the reading is 1.026.

make sure the screw used for calibration is tight after you calibrate.

[drparker]

I've got the DRs F&S unit with ATC they put it on sale for $40 every so often. After intial calibration I've only had to change it once in three years, after my kid dropped it. Still check it every 2 months with PinPoint Cal solution and it's dead on everytime.