How to read hydrometer?

Notsolostfish · Oct 15, 2023

Whats that represent to? The black dot is 5? Right? So is that 1.0255?

Subsea · Oct 15, 2023

Not familiar with that brand. I agree that if the manufacture left off 1.0 then you would read
1,0255 specific gravity.

EricR · Oct 15, 2023

Yes but you use the flat water level as opposed to where it bulges up right around hydrometer,,, so I'd say 1.0256 if I'm seeing it right.

BeanAnimal · Oct 15, 2023

1.0256
Take water temp of the sample when read and apply adjustment table or equation provided by the manufacturer.

EricR · Oct 15, 2023

BeanAnimal said:
1.0256
Take water temp of the sample when read and apply adjustment table or equation provided by the manufacturer.

True about temperature correction but, in practice, you have to be quite a few degrees away from 77 for it to make a truly significant difference, in my opinion. (I'm making the huge assumption that this is the Tropic Marin hydrometer calibrated to 77 degrees and most people run 77-78ish, however)
*so good point

EeyoreIsMySpiritAnimal · Oct 15, 2023

Hatedfish said:
Whats that represent to? The black dot is 5? Right? So is that 1.0255?

Yep! (The dot is 1.0255, your reading is a thousandth or 2 higher)

*Sorry, 4 decimal places is ten thousandths...

Notsolostfish · Oct 15, 2023

EeyoreIsMySpiritAnimal said:
Yep! (The dot is 1.0255, your reading is a thousandth or 2 higher)

*Sorry, 4 decimal places is ten thousandths...

So im guessing i just have to convert 1.0255 to my temperature 78F?

EeyoreIsMySpiritAnimal · Oct 15, 2023

Hatedfish said:
So im guessing i just have to convert 1.0255 to my temperature 78F?

No need to worry about 1 degree.

Notsolostfish · Oct 15, 2023

EeyoreIsMySpiritAnimal said:
No need to worry about 1 degree.

Okay so technically my salinity right now is 1.0255?

EeyoreIsMySpiritAnimal · Oct 15, 2023

EeyoreIsMySpiritAnimal said:
No need to worry about 1 degree.

1.0256 at 78 degrees is 1.026

EeyoreIsMySpiritAnimal · Oct 15, 2023

Hatedfish said:
Okay so technically my salinity right now is 1.0255?

Functionally, 1.0255 at 78 degrees is perfect. Technically, it's just under 1.026

BeanAnimal · Oct 15, 2023

Don't use the conversion chart at BRS or that floats around here that came from BRS it is WAY off.
This one is correct

BeanAnimal · Oct 15, 2023

EeyoreIsMySpiritAnimal said:
1.0256 at 78 degrees is 1.026

I guess it depends on where you want to run.

I suggest anybody who is using ICP to run at 35ppt (1.0264 at 25c/77c) - as It is my understanding that they calibrate to 35ppt. I am not sure which ICP companies scale their results or how they compensate if the sample is not 35ppt.

I think opinions vary on what the ideal salinity is otherwise and there are good arguments for a lot of values. I try to keep 35ppt now - but for years ran 33 or 34 and sometimes far lower when there was no SPS in the tank.

I would say for somebody who has room and tank that keep a fairly stable temp, then compensation is likely not a factor.

For somebody who has a tank and or room that fluctuates a lot and runs ATO and automated sampling (salinity swings that need to be managed), then readings can easily be 2ppt off high or low (defeating the purpose of the precision hydrometer) and making tracking kind of messy as sample temperature and tank salinity swing.

EeyoreIsMySpiritAnimal · Oct 15, 2023

BeanAnimal said:
I guess it depends on where you want to run.

I suggest anybody who is using ICP to run at 35ppt (1.0264 at 25c/77c) - as It is my understanding that they calibrate to 35ppt. I am not sure which ICP companies scale their results or how they compensate if the sample is not 35ppt.

Really?? Are you going to pick apart every post I make from now on?

His reading is 1.0256 (as far as I can see).

He asked what his salinity was with temp correction.

I used the exact chart you posted and did the conversion for him.

I was not telling anyone what salinity to use.

EricR · Oct 15, 2023

BeanAnimal said:
Don't use the conversion chart at BRS or that floats around here that came from BRS it is WAY off.
This one is correct

I agree that some of the charts I've seen look WAY off and this one looks better.
I would've preferred this one to have units presented differently:
- Temp in Farenheit (although easy enough to convert)
- Corrected values in SG instead of ppt -- I assume this was done to conserve space but could've easily just left off the 1.02 part and presented just the last 2 digits (if that made sense)

I take no responsibility for the accuracy of this website (since I don't bother temp correcting) but have seen this one recommended, and it's easy to use:

Salinity Correction

BeanAnimal · Oct 15, 2023

Yes his reading appears to be 1.0256

I didn't accuse you of anything. I just added context for the OP. As you know, the relationship between salinity and specific gravity (and conductivity) is actually pretty complex and can be confusing for even well seasoned aquarists.

BeanAnimal · Oct 15, 2023

EricR said:
I take no responsibility for the accuracy of this website (since I don't bother temp correcting) but have seen this one recommended, and it's easy to use:

Salinity Correction

It is accurate.

If you are interested in how it was developed and the problems encountered with the math, there is a fairly lengthy ancient thread at RC where several of us old timers (I can't remember if I participated in that conversation or just creeped) discussed the mathematics and rather confusing context of the conversions. I think Randy and several others contributed.

There is another very good and accurate calculator here:

Salinity calculator

A unit converter for calculating salinity in marine aquariums. The calculator supports conductivity (mS/cm), salinity (PSU og ppt), density (g/cm³) og specific gravity.

reefapp.net

I had the same basic calculator on my site as well, but it has been down along with the siphon flow calculator since Flash became deprecated. I have rebuilt some of the calculators, but those have yet to be done and I may never get to them.

BeanAnimal · Oct 15, 2023

EeyoreIsMySpiritAnimal said:
Really?? Are you going to pick apart every post I make from now on?

There is no need to be combative. I didn't pick anything apart, say you were wrong or accuse you of anything.

I entered this thread before you and further added to the conversation by responding to your post after you did. I don't know you or follow you and couldn't tell you how many threads we have shared or interacted in other than this and I think one yesterday regarding my overflow (where you also got kind of defensive and combative). It sounds like you have a problem with me, not the other way around

In any case, If you didn't mean to say 1.0255 at 78 is the perfect salinity - then you may want to reword your post, as that is how it read.

Likewise, even if you were trying to convey that 1.0255 at 78 IS perfect... that is a perfectly valid opinion anyway.

Either way, I simply added to the conversation for the OPs benefit. I quoted your post so that my comments had context.

Relax and try to be a bit less sensitive, nobody is out to get you.