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2 refractometers with different readings

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Zack801 View Drop Down
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    Posted: July 18 2017 at 8:40pm
I have two almost identical refractometers at home both are ATC. Out of curiosity I tried one that had been sitting a while and my tank measured 1.022. I had a brief moment of panic since any water I mix is 1.025-.026. I tried my other meter and it was closer to 1.025 possibly a little under. I recalibrated both using rodi water and zeroed them out with the screw. Retested the tanks with similar results. Does anyone have any ideas? I'd love to trust the meter that I reading higher because it really makes the most sense but I'd like any other thoughts or suggestions as well
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Krazie4Acans Quote  Post ReplyReply Direct Link To This Post Posted: July 18 2017 at 9:06pm
Why would you calibrate them at 0 when you want them accurate at the salinity if your tank? Wouldn't it make more sense to calibrate them with the correct fluid of 1.025 like the manufacturer recommends?  Then they are accurate at the value you are going to achieve and not at a value that we all hope to never see when testing our tanks.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Zack801 Quote  Post ReplyReply Direct Link To This Post Posted: July 18 2017 at 9:09pm
Maybe calibrating is the wrong term? I insured it was zeroed (in case this was causing any higher/lower readings) is this not correct? Is there some sort of calibration fluid people use the "calibrate" these?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Zack801 Quote  Post ReplyReply Direct Link To This Post Posted: July 18 2017 at 9:17pm
So as soon as I read your reply and responded I started reading more into it. I guess there is actually calibration fluid that I can use.... are there any places locally I could buy this or just online? I also came across a diy solution by Randy Holmes Farley if anyone has tried that?I've had tanks successfully up and running without issues for near a year at this point so I wonder how off the salinity really could be? I honestly thought I just had to zero it out with rodi water and that was it... I guess I learn something new everyday

Edited by Zack801 - July 18 2017 at 9:21pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Krazie4Acans Quote  Post ReplyReply Direct Link To This Post Posted: July 19 2017 at 10:10am
I got some at Aquatic Dreams but I'm not sure if there are any of the Salt Lake stores that stock it. If the stores don't have it Amazon has it and if you are a prime member you can have it by Friday.

I know there are people that zero theirs and it works but knowing that these devices are only accurate to +- 3% at best I want them to be the most accurate in the range I will be measuring. Due to that I have always used the calibration solution for mine.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Zack801 Quote  Post ReplyReply Direct Link To This Post Posted: July 19 2017 at 10:13am
Sweet yeah I ended up ordering some last night on amazon and I'm holding off on my water change so I can re check the tanks and now the new water. Say it is that low 1.022 is it better to stop fresh water ato and maybe just top off with 1.025 and checking until the levels come back up?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Krazie4Acans Quote  Post ReplyReply Direct Link To This Post Posted: July 19 2017 at 12:38pm
Yes that is a great way to raise it. Slowly raise it for sure. Do not dump salt straight into the tank or sump to try and correct it. LOL

You can also do water changes and remove less water than you add. Your sump level might be slightl high for a day or so but as the evap happens the salinity will slowly rise.


Edited by Krazie4Acans - July 19 2017 at 12:39pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Reefboy4life Quote  Post ReplyReply Direct Link To This Post Posted: July 19 2017 at 1:55pm
I have always hated my refractometer
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Zack801 Quote  Post ReplyReply Direct Link To This Post Posted: July 19 2017 at 1:56pm
How do you measure salinity?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mark Peterson Quote  Post ReplyReply Direct Link To This Post Posted: July 19 2017 at 6:18pm
I'm not sure how many of you check all new threads/posts in the General Discussion and similar informational sections like I do. You should. I learn something new there almost every day. The recent thread linked below is one such. It contained important info about testing kits, but also included information about checking salinity, very pertinent to this thread:

Aloha,
Mark  Hug
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mark Peterson Quote  Post ReplyReply Direct Link To This Post Posted: July 20 2017 at 10:29am
Originally posted by Krazie4Acans Krazie4Acans wrote:

Do not dump salt straight into the tank or sump to try and correct it. LOL
Defintely do not sprinkle salt into the tank, but, adding salt to the sump is a great way to raise salinity if done in moderation, not too close to the return intake and while monitoring salinity in the display. Salt can be poured into the filter bag, if used. The key is not to raise salinity too quickly. Though it can be raised faster without long term problems, it's usually best not to raise salinity any faster than about .001 unit of SG per hour. Raising from 1.022 to 1.025 would take 3 hours, though I must admit, I've done it quicker than that. Wink 

Lowering salinity quickly is less of a problem. Maybe because the animals are genetically built to handle a dump of lots of freshwater during a storm.

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Mark  Hug
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Post Options Post Options   Thanks (0) Thanks(0)   Quote phys Quote  Post ReplyReply Direct Link To This Post Posted: July 21 2017 at 4:21am
The reason to calibrate near your testing point is due to errors in the manufacturing that grow as you move away from your measuring point. Think of it as having a ruler that is off by 1/10 of an inch but you have to measure something 30 feet away. Buuut you really only care about measuring a foot away from the point that is 30 feet away. If you start where you stand, your error is greater than if you walked 30 feet to be near the point you actually care to measure. The difference is 3 inches of error at 30 feet, or 1/10 of an inch at one foot.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mark Peterson Quote  Post ReplyReply Direct Link To This Post Posted: July 21 2017 at 8:37am
I like that explanation and analogy. Thanks Paul

Is this crazy or what. Wacko   For as long as I've been keeping reef aquariums, I have been checking salinity(specific gravity) with refractometers and hydrometers that were reading high by as much as 0.008. Shocked

Twenty years ago, before the hobby bloomed, we all learned that the recommended tank water salinity was 1.022 SG. This means we may have been keeping it as low as 1.014. Crazy huh!

You know what though, as bad as this may seem, it's really not bad at all. It actually proves what I have always said, that when it comes to salinity, we needn't worry much about exactness/accuracy/precision.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Zack801 Quote  Post ReplyReply Direct Link To This Post Posted: July 23 2017 at 1:45pm
So I've got both calibrated now. One thing to note is they were very close to the same readings I got when I tested after zeroing these with plain rodi water. As far as raising salinity do you just donwater changes with the corrected amount I.e 1.025? Or would you make a batch with slightly higher salinity and slowly add that?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mark Peterson Quote  Post ReplyReply Direct Link To This Post Posted: July 23 2017 at 6:13pm
That depends.
What salinity was the tank before calibration and what is it now?
Have coral been okay?
Have there been any other issues in the tank?

Aloha,
Mark  Hug

P.S.
When salinity is raised, Alk, Ca, Mg, etc. also rise by the same percentage because their concentration in the water is higher. It's a small percentage though. Raising SG from 1.022 to 1.025 is only 2.94%


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Post Options Post Options   Thanks (0) Thanks(0)   Quote Zack801 Quote  Post ReplyReply Direct Link To This Post Posted: July 23 2017 at 7:21pm
Tank was actually the same before and after 1.022. Everything has been fine as well if just like to adjust to what I was thinking it was originally. I don't have much salt creep, what else causes salinity to drop over time?
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