RO Salinity less than 0?

[907_Reefer]

Hey all, recently noticed when testing salinity on my RODI (BRS 4 stage, 8 months old), I'm getting less than 0 readings with a freshly calibrated Vee Gee Scientific refractrometer, where I used to get exactly 0 on my RO. Calibrated 3x now, same deal. All fluids at room temp ~68 F, refractrometer cleaned with RODI after each test..

EDIT: Tank temperature during reading is 78 F, RODI and 35ppt are room temp 68 F.

Calibration using 33ppt fluid right around 1.0264:

Tank level, ~1.025 as intended:

RODI made within a few days ago:

What gives?!

 

[feresadas]

My only thought would be if you are using a calibration fluid with a screw cap, over time that will evaporate some out and you will raise the salinity very slowly every time you open it? causing you to calibrate incorrectly? how old is your calibration fluid and how do you store it?

 

[reefiniteasy]

Are you calibrating with distilled as the VeeGee manual says? That’s what I do and have never had an issue. Only thing I can think of.

 

[907_Reefer]

My only thought would be if you are using a calibration fluid with a screw cap, over time that will evaporate some out and you will raise the salinity very slowly every time you open it? causing you to calibrate incorrectly? how old is your calibration fluid and how do you store it?

Good idea, I use Fritz currently with a screw cap, opened up and it is pretty clean though. Gave it an RO bath for good measure, but while I had it opened I pulled some with a fresh dropper and get the same 1.0264.. I store it in the stand, 55 gal no sump, no equipment in there so it stays dark and room temp (62-68F here in AK). No storage instructions are on the bottle..

EDIT: 35ppt solution is about 7 months old. Ordered another bottle from Amazon today also for good measure.

Are you calibrating with distilled as the VeeGee manual says? That’s what I do and have never had an issue. Only thing I can think of.

I have not been using distilled but will pick some up this week for good measure, good idea here as well.

 

[Cthulukelele]

Yeah the first use you calibrate the line to 0 using your ro water. There's a little nut in the center and a screwdriver to calibrate included with the box.

 

[907_Reefer]

Yeah the first use you calibrate the line to 0 using your ro water. There's a little nut in the center and a screwdriver to calibrate included with the box.

Yep yep I'm familiar, but it is not always recommended to use RO for calibration - I have been using the 35ppt, my RO has been showing at 0 for 8 months but ran a check initially last week, 35ppt at 1.0264 and RO at -0.04, same today..

 

[Cthulukelele]

Yep yep I'm familiar, but it is not always recommended to use RO for calibration - I have been using the 35ppt, my RO has been showing at 0 for 8 months but ran a check initially last week, 35ppt at 1.0264 and RO at -0.04, same today..

They're notoriously finicky to read, and even though people describe refractometers as taking the guesswork out of salinity, even slightly shifted angles can lead to different readings

 

[Cthulukelele]

Yep yep I'm familiar, but it is not always recommended to use RO for calibration - I have been using the 35ppt, my RO has been showing at 0 for 8 months but ran a check initially last week, 35ppt at 1.0264 and RO at -0.04, same today..

Also any temp swings in that time? Temperature swings greater than 20-30 degrees can majorly affect readings

 

[907_Reefer]

They're notoriously finicky to read, and even though people describe refractometers as taking the guesswork out of salinity, even slightly shifted angles can lead to different readings

Yea I've done about 5 calibration checks now and 10 readings otherwise, seeing these numbers consistently.

Also any temp swings in that time? Temperature swings greater than 20-30 degrees can majorly affect readings

No temp swings and I've been using the same salt mix quantity for 1.025 SG water changes weekly, been giving the same readings for the same mix each time. Just randomly checked RO last week and the negative threw me for a loop, so I began recalibrating, no changes.

If the 35ppt is off, that would put the tank at 1.029 or so... FTS today, only issue I've been dealing with is high phosphates and hair/bubble algea..

No filter:

Orange filter:

 

[Cthulukelele]

Yea I've done about 5 calibration checks now and 10 readings otherwise, seeing these numbers consistently.



No temp swings and I've been using the same salt mix quantity for 1.025 SG water changes weekly, been giving the same readings for the same mix each time. Just randomly checked RO last week and the negative threw me for a loop, so I began recalibrating, no changes.

If the 35ppt is off, that would put the tank at 1.029 or so... FTS today, only issue I've been dealing with is high phosphates and hair/bubble algea..

No filter:

Orange filter:

Do you heat both your ro water reservoir and your salt water reservoir to the same temperature? Higher temp water leads to higher refractometer readings typically.

It's not entirely out of the question for tanks to look healthy still at 1.028-1.029 as long as no huge swings. Hard to say honestly. I was accidentally running at nearly 1.028 when my tank looked its healthiest.

BTW beautiful tank

 

[907_Reefer]

Do you heat both your ro water reservoir and your salt water reservoir to the same temperature? Higher temp water leads to higher refractometer readings typically.

It's not entirely out of the question for tanks to look healthy still at 1.028-1.029 as long as no huge swings. Hard to say honestly. I was accidentally running at nearly 1.028 when my tank looked its healthiest.

BTW beautiful tank

My RO reservoirs (buckets) do not get heated, but my SW mix is heated to 78 before water changes, and test against the tank to be sure SG matches @ 1.025 @ 78 F.

For good measure now I'm warming a bucket of RO to test at 78, will report back. Good excuse to give the 3 gal beta tank a WC also.

Thanks for the tank comment! It's getting ready for a 300 mile move to our new house in a week or so, cross your fingers.... Documenting that in my build thread.

 

[Pistondog]

Calibrate with ro water. Focus the eyepiece and make sure the cover sits squarely on the glass. My veegee is 4 years old, the hinge is rusting and needs to be forced to be flat on glass.

 

[reefiniteasy]

Calibrate with ro water. Focus the eyepiece and make sure the cover sits squarely on the glass. My veegee is 4 years old, the hinge is rusting and needs to be forced to be flat on glass.

In case you want to replace the cover.

Refractometer Replacement Daylight Plate Kit

Buy Refractometer Replacement Daylight Plate Kits from VEE GEE Scientific today! Order Online for Free Shipping & Fast Delivery.

www.veegee.com

 

[907_Reefer]

The verdict is in on 78 F RO, same reading as 68F RO.. My 35ppt must be bad?! I guess logically if some of the 35ppt has evaporated it would read higher eh...

Did a WC today with "1.0235" on the "calibrated" refractrometer, to be safe, which put the tank at "1.024" (or 1.027 est re bad fluid). Will grab some distilled this week and have new 35ppt on the way and will report back.

78F RO today:

This reminds me of a pirate joke, where he enters a bar, sits down, with his ship steering wheel in his pants. Bartender says, what's up with that steering wheel? He says, "Yarrr, it's drivin' me nuts!!"

I'll be here all week.

 

[907_Reefer]

Wanted to update the thread here, I picked up some distilled and found my old RTS10ATC refractrometer also! That one was used on our old tank until 2013, 10 years ago - been in storage since..

Popped some distilled in it, 0! Tested tank water, 1.028. Tested 35ppt, 1.031..... 10 years ago I was calibrating with distilled.

So, both refractrometers essentially match but ~0.004 off on all levels as one had been calibrated with 35ppt and one with distilled (10 years ago). If I calibrate the old one down to 1.0264 for 35ppt it will also being the RO down to -.004 and the tank to 1.024.

With so many people calibrating on RO, how many tanks are ~.003-4 off from what they think?!

Distilled (matches my RO readings), old refractrometer:

35ppt:

Tank: