refractometer always needs adjustments

[PDXreefer]

I test my water twice a week and every time I check calibration, it's off. Do they typically go out of calibration that fast??

[AZRippster]

Some do and they are sensitive to heat changes. At least in my experience that has been the case. One of the primary reasons I purchased a Milwaukee.

[lmm1967]

Mine does need calibration at least 50% of the time. I also noticed - contrary to what everyone will tell you - I can calibrate to Zero using RO water and it is accurate (verified multiple times using calibration solution) at 1.025.

I mainly only use it to compare new SW with tank water right before a water change though.

My ATO seems to keep salinity really stable in the tank.

[PDXreefer]

Hum, maybe I should buy a better one?

[125mph]

Originally Posted by PDXreefer

Hum, maybe I should buy a better one?

Maybe!

My first refractometer needed calibration before each use.. it was very annoying.. The screw eventually rusted and I brought another one from a LFS. I've been using that new one over a year and its always dead on.. I was wondering maybe something was wrong and tested with calibration fluid but its DEAD ON and still doesnt need calibration.. Best $40 bucks ever!!

Both refractometers look identical.. I think different brand and different quality.

[125mph]

Originally Posted by lmm1967

Mine does need calibration at least 50% of the time. I also noticed - contrary to what everyone will tell you - I can calibrate to Zero using RO water and it is accurate (verified multiple times using calibration solution) at 1.025.

.

I think the calibration fluid is a marketing technique to get us to spend more money... I've always calibrated my refractometer using RO water.. Then I read thats not good and my salinity could be way off, so I rush ordered the the calibration fluid.. its dead ON!

I talked to the LFS and they say they never heard of calibration fluid and always calibrate with RO water. In fact, they've done that for years. I tested their water with refractometer and its also dead on... 1.025! If there was any slippage by calibrating with RO water, it would have happen to them by now.

[smatter]

Get a lab grade glass hydrometer.

[Optionman]

this is what you want to get!

https://www.amazon.com/Milwaukee-MA8.../dp/B007Z4ITWU

[GimpyFin]

+1 to Optionman's suggestion. The Milwaukee digital refractometers are excellent (If you are looking at options for a better one.) Probably the best $100 I've spent in this hobby. Very easy to use and you calibrate them with ro/di or distilled water, you don't need a solution. I'll re-calibrate it periodically just for good measure (Done it maybe a handful of times in 3 years), but it stays accurate and calibrated quite well.

[ericarenee]

Originally Posted by smatter

Get a lab grade glass hydrometer.

1+


Why use testing equipment has has to be tested before you can use it to test..

i have a hydrometer swing arm that i use for quick test and once in a while i will confirm it with a glass one

[PDXreefer]

I've heard/read that hydrometers are not as accurate.

[ericarenee]

Originally Posted by PDXreefer

I've heard/read that hydrometers are not as accurate.

The people who want you to spend more money are the people who tell you that...

and its actually not about being perfect its about having consistent results

[smatter]

High quality glass hydrometers are very accurate. I'm not talking about the cheap ones with the built-in thermometer. Check out Tropic Marin's offering. Conductivity is also an option.

[ajm83]

How long are you leaving it to settle after putting the droplets on the lens thingy?

I have a temp compensated model but I still have to leave mine a good 10 mins or so before it gives accurate results.

[outssider]

the smallest temperature change (room temperature) will cause my refractometer to need calibration. also, it is way off when I calibrate with ro/di water.

[kurt_n]

Originally Posted by 125mph

I think the calibration fluid is a marketing technique to get us to spend more money... I've always calibrated my refractometer using RO water.. Then I read thats not good and my salinity could be way off, so I rush ordered the the calibration fluid.. its dead ON!

I talked to the LFS and they say they never heard of calibration fluid and always calibrate with RO water. In fact, they've done that for years. I tested their water with refractometer and its also dead on... 1.025! If there was any slippage by calibrating with RO water, it would have happen to them by now.

It all depends on the refractometer. Sounds like you got lucky and have one that reads very linear between 1.000 and 1.025.

Calibration fluid isn't a gimmick, it's good insurance.

To truly calibrate something, you need two points of reference and those points of reference should bracket the value you're trying to measure. When you calibrate a pH meter, you use 7.0 and 10.0 reference solutions. Those solutions establish known data points below and above the value you're measuring. The meter can then do the math (adjusting the zero and the slope of the assumed linear equation) between those two values to give you a pretty exact pH value.

That's not the case with a refractometer. You can only adjust the zero of the refractometer, which means you can only use one point of reference. If you only get one reference point, why not make it as close as possible to what you're actually measuring? That way, if the linearity of your refractometer is not accurate (the "slope" part of the linear equation), it won't mess with your reading much. If you're measuring sea water, the best reference would be the calibration fluid that simulates sea water. If you're interested in measuring RO/DI water, then by all means use that to calibrate.

No matter what the device, if you can only calibrate using a single point, your best bet is to make that point as close to the number you're measuring as possible.

[125mph]

Originally Posted by kurt_n

It all depends on the refractometer. Sounds like you got lucky and have one that reads very linear between 1.000 and 1.025.



Calibration fluid isn't a gimmick, it's good insurance.



To truly calibrate something, you need two points of reference and those points of reference should bracket the value you're trying to measure. When you calibrate a pH meter, you use 7.0 and 10.0 reference solutions. Those solutions establish known data points below and above the value you're measuring. The meter can then do the math (adjusting the zero and the slope of the assumed linear equation) between those two values to give you a pretty exact pH value.



That's not the case with a refractometer. You can only adjust the zero of the refractometer, which means you can only use one point of reference. If you only get one reference point, why not make it as close as possible to what you're actually measuring? That way, if the linearity of your refractometer is not accurate (the "slope" part of the linear equation), it won't mess with your reading much. If you're measuring sea water, the best reference would be the calibration fluid that simulates sea water. If you're interested in measuring RO/DI water, then by all means use that to calibrate.



No matter what the device, if you can only calibrate using a single point, your best bet is to make that point as close to the number you're measuring as possible.

Funny thing, I just checked my calibration fluid again and the refractometer was way off lmao. I thought my tank was 1.025 but it's actually 1.023. I triple checked it. Then I ran the rodi test and it was measuring under 1.00 which is the opposite direction I was expecting.

I then read about the slope error issue from randy's article. Makes sense, similar to calibrating PH probes.


Sent from my iPhone using Tapatalk

[mikeatjac]

Originally Posted by 125mph

I think the calibration fluid is a marketing technique to get us to spend more money... I've always calibrated my refractometer using RO water.. Then I read thats not good and my salinity could be way off, so I rush ordered the the calibration fluid.. its dead ON!

I talked to the LFS and they say they never heard of calibration fluid and always calibrate with RO water. In fact, they've done that for years. I tested their water with refractometer and its also dead on... 1.025! If there was any slippage by calibrating with RO water, it would have happen to them by now.

i would not use an LFS that had never heard of calibration fluid. Pretty common item weather you use it or not.

[Ou8me2]

I might be crazy but I had this issue at first. I learned only adding 2 drops of the fluid to calibrate and then when testing use 2 drops of tank water. If you put a ton of fluid on it will read differently each and every time depending on how much water or fluid you use. Also if you use an ATC refractometer they recommend waiting 45 seconds to read the results or at least mine does anyways. Hope that makes sense. Ever since I use 2 drops it has been rock solid accurate for me.

[Kyuss]

Originally Posted by 125mph

I think the calibration fluid is a marketing technique to get us to spend more money...

That's some scam. They get you, for what $7, every 5+ years!

[125mph]

Originally Posted by Kyuss

That's some scam. They get you, for what $7, every 5+ years!

That's the start. Next, you'll need enhanced refractometer fluid harvested straight from the Red Sea!


Sent from my iPhone using Tapatalk