Help with salinity measuring

[saulgoodmannnn]

I purchased a reef tank second hand that was well established. The guy I picked it up from said he didn’t measure salinity because he just always removed exactly 4.5 gallons and replaced exactly 4.5 gallons. He said every time he measured he got inconsistent measurements. Well I see the struggle now. I have a Milwaukee MA887 as well as two hydrometers. I watched BRS’s video on the salinity tester and it says to not measure with multiple devices-stick with one and stay with it.
My issue is since my latest water change outside the typical 4.5G my RBTA has shrunk up lost all its color and is now brown.

My parameters are all stable the only thing I can think of is salinity… what should I do? What do you guys do to get an accurate salinity measurement?

if it helps here’s my parameters

Alk	9.2
Calc	461
Ph	7.9 @75.5 degrees
Phosphate	.43 (have to change my socks) usually is .14 to .24
Magnesium	1380-1410
Salinity	1.028 @ 75 degrees

 

[PeterEde]

Add RODI water to slowly drop salinity down to 1.026/1.025
Would be my advice. But I've only been at this 2 months as well.

I'm keeping my PH at 8.3 and ALK at 10

 

[saulgoodmannnn]

I usually have my tank at 10 Alk but after my last water change I think it was too high in salinity and it boosted all my parameters. I’ve been letting them creep back down to minimize stress on the corals. Ideally I would like my Alk to be 10, Calc 450 Mag 1350 and ph 8.3 but idk how accurate my Hannah ph probe is I always calibrate it before checking so ‍♂. I can keep everything stable as long as my equipment is accurate

 

[Rmckoy]

Slowly add rodi water to lower salinity to 1.025-1.026

salinity is too high

 

[MaxTremors]

I would trust the Milwaukee over the swing arm hydrometers (they are notorious for being wildly inaccurate), I don’t know much about the Milwaukee testers, does it need to be calibrated? I would maybe just get a quality refractometer. You should slowly, over several days lower the salinity to 1.026, each day you can take out 3-4 cups of saltwater and replace with RODI, and keep this up until you get to 1.026. I would definitely recommend checking the salinity of your water change water to ensure it matches your tank (you can go slightly lower if you’re still trying to lower the salinity in your tank).

Other than that, your phosphates are really high, which could be why your anemone is losing color, they should be between 0.03 and 0.08ppm, so you’re 5-10x over where it should be. What are your nitrates? I would suggest changing your socks every 2-

As far as your alkalinity, I would keep it wherever your preferred salt mix mixes to. Personally, I try to keep mine around 8.5, NSW is around 7, I haven’t ever really found a good reason to keep it any higher than 9 or so, it’s been said hard corals grow faster at higher Alk, but that you get better colors at lower Alk. So it’s kind of personal preference, stability is what’s important, just pick a number (7-12) and stay there.

 

[LeftyReefer]

I recently picked up a Hanna HI98319 Salinity Tester and now I'm wondering why I didn't get one much sooner. Love that thing.

 

[Dennis Cartier]

I would suggest getting an accurate floating hydrometer. The Tropic Marin High Precision ones are very good for cross checking results. This is the one I would suggest High Precision Hydrometer.

The electronic ones can go out of calibration, so having a source that does not require calibration for reference is a good idea.

The swing arm ones are not particularly accurate as you have probably found out.

Dennis

 

[elcapitan1993]

1.028 is to high, I would slowly bring it down to 1.026 at least, I keep my salinity stable using the Milwaukee as well, did you test it to make sure it isn’t reading 0.002 SG higher or lower? That is they’re error margin

 

[Randy Holmes-Farley]

Note: the milwaukee only claims accuracy to +/- 0.002 in sg, so 1.028 might be 1.026 to 1.030. It may not be too high.

IMO, the first step is to convince yourself the Milwaukee is accurate by testing it.

I assume you have calibrated it with RO/DI?

Assuming so , then move on to checking it with a DIY standard seawater mix, as described here:

Reef Aquarium Salinity: Homemade Calibration Standards by Randy Holmes-Farley - Reefkeeping.com

 

[elcapitan1993]

Note: the milwaukee only claims accuracy to +/- 0.002 in sg, so 1.028 might be 1.026 to 1.030. It may not be too high.

IMO, the first step is to convince yourself the Milwaukee is accurate by testing it.

I assume you have calibrated it with RO/DI?

Assuming so , then move on to checking it with a DIY standard seawater mix, as described here:

Reef Aquarium Salinity: Homemade Calibration Standards by Randy Holmes-Farley - Reefkeeping.com

That why the Hanna salinity pen is better because it’s not a refractometer it’s a conductivity probe so it will read the salt unlike a refractometer that reads other stuff and adds it to your total salinity

 

[Randy Holmes-Farley]

That why the Hanna salinity pen is better because it’s not a refractometer it’s a conductivity probe so it will read the salt unlike a refractometer that reads other stuff and adds it to your total salinity

While that underlying statement is technically correct, I do not think there is any detectable impact on salinity measurement via refractometer from "other stuff" in seawater.

What "other stuff" are you concerned that refractometer is reading?

 

[elcapitan1993]

While that underlying statement is technically correct, I do not think there is any detectable impact on salinity measurement via refractometer from "other stuff" in seawater.

What "other stuff" are you concerned that refractometer is reading?

This is just what Hanna told me when I contacted them about the pen reading 0.001 different then my Milwaukee

 

[Randy Holmes-Farley]

This is just what Hanna told me when I contacted them about the pen reading 0.001 different then my Milwaukee

They are mistaken.

 

[X-37B]

I prefer the TM floater for SG measurments.
I have a refractometer and a swing arm.
I do not use the refrac much any more.
I do use the swingarm for a quick spot check.
I know what the swingarm reading is vs the TM and it is always different. With that, on my swingarm, 1.026 is actualy 1.025 on my TM floater.
Make sure all bubbles are off the arm.
Its always good to have a way to cross check any test you do, imo.

 

[Uncle99]

What’s nitrate.
Flux in nitrate quickly would surely make a nem, unhappy.
Refractometer, calibrated, stick to that.
Easy to replicate, time after time.

 

[FiddlersReef]

I would suggest getting an accurate floating hydrometer. The Tropic Marin High Precision ones are very good for cross checking results. This is the one I would suggest High Precision Hydrometer.

Totally recommend this. I got one on a whim, just because I thought it was cool. But omg is it so precise I just enjoy using it. I picked up a 500 ml cylinder to use with it, and now it's the only way I check anymore. It takes a minute longer than using a refractometer, but it's 100% accurate and never needs to be recalibrated.

And again... it's just cool.

 

[elcapitan1993]

They are mistaken.

Here is a picture of a post on why they claim this and here is the Link , this is the exact thing they said to me as well

 

[Randy Holmes-Farley]

Here is a picture of a post on why they claim this and here is the Link , this is the exact thing they said to me as well

You are certainly correct that that is what they claim there, and they are certainly wrong to claim it. Sad, really, that such a company would make such an unforced error. I hope it is ignorance and not simple falsehood to push their product.

There are pros and cons to all methods of salinity measurement, but interference by "other things" IS NOT one of them for any method reefers use. There are several reasons to prefer conductivity (it is my preferred method as well), but interference by organics and such isn't in the cards.

At its nitty gritty core, one even has to challenge if the premise is correct that organics are not part of salinity. By the original definition of salinity (solids per kg of seawater), they are.

Fortunately, organics are too low in concentration in seawater to have anything like the effect claimed above.

Let's explore how nutso this idea is, and we'll take ethanol as an example to see how much would be needed in the water to get 34 ppt seawater sg = 1.0256 to falsely read as 35 ppt seawater with sg = 1.0264.

From my article below, we see that:

34 ppt refractive index = 1.33922
35 ppt refractive index = 1.33940
difference = 0.00018

Reef Aquarium Salinity: Homemade Calibration Standards by Randy Holmes-Farley - Reefkeeping.com

Thus, all we need to do is see how much ethanol will raise the refractive index of water by 0.00018

There are lots and lots of online references.

Let's take this one:

Refractive index of ethanol solutions.

Refractive index of ethanol solutions,

www.refractometer.pl

2% ethanol raises the refractive index by 1.3342 - 1.3330 = 0.0012

That is 6.6 fold higher than the 34 to 35 ppt error calculated above.

Thus, it takes 6.7 times less, or 2% ethanol/6.6 = 0.3% ethanol.

So, how much organic matter in the form of ethanol is needed to give a false high reading by refractive index of 1 ppt? 0.3%. That's not 0.3 ppm, it is 3,000 ppm!

In a 100 gallon (378.5 L) aquarium, you'd need to add about 1.1 liters of pure ethanol, or 2.8 liters of vodka. lol

Looked at differently, how much organic matter is in a reef tank or in the ocean?

About 1 ppm organic carbon in the ocean, and in reef tanks:

Total Organic Carbon (TOC) and the Reef Aquarium: an Initial Survey, Part I

Department of Chemistry, The Pennsylvania State University, University Park, PA 16802. Ken and Kelly report on their work on Total Organic Carbon and how it relates to the reef aquarium.

reefs.com

Thus, there is about 3,000 times too little organic matter in a reef tank to cause a difference of 1 ppt in salinity measurement by refractive index.

 

[elcapitan1993]

You are certainly correct that that is what they claim there, and they are certainly wrong to claim it. Sad, really, that such a company would make such an unforced error. I hope it is ignorance and not simple falsehood to push their product.

There are pros and cons to all methods of salinity measurement, but interference by "other things" IS NOT one of them for any method reefers use. There are several reasons to prefer conductivity (it is my preferred method as well), but interference by organics and such isn't in the cards.

At its nitty gritty core, one even has to challenge if the premise is correct that organics are not part of salinity. By the original definition of salinity (solids per kg of seawater), they are.

Fortunately, organics are too low in concentration in seawater to have anything like the effect claimed above.

Let's explore how nutso this idea is, and we'll take ethanol as an example to see how much would be needed in the water to get 34 ppt seawater sg = 1.0256 to falsely read as 35 ppt seawater with sg = 1.0264.

From my article below, we see that:

34 ppt refractive index = 1.33922
35 ppt refractive index = 1.33940
difference = 0.00018

Reef Aquarium Salinity: Homemade Calibration Standards by Randy Holmes-Farley - Reefkeeping.com

Thus, all we need to do is see how much ethanol will raise the refractive index of water by 0.00018

There are lots and lots of online references.

Let's take this one:

Refractive index of ethanol solutions.

Refractive index of ethanol solutions,

www.refractometer.pl

2% ethanol raises the refractive index by 1.3342 - 1.3330 = 0.0012

That is 6.6 fold higher than the 34 to 35 ppt error calculated above.

Thus, it takes 6.7 times less, or 2% ethanol/6.6 = 0.3% ethanol.

So, how much organic matter in the form of ethanol is needed to give a false high reading by refractive index of 1 ppt? 0.3%. That's not 0.3 ppm, it is 3,000 ppm!

In a 100 gallon (378.5 L) aquarium, you'd need to add about 1.1 liters of pure ethanol, or 2.8 liters of vodka. lol

Looked at differently, how much organic matter is in a reef tank or in the ocean?

About 1 ppm organic carbon in the ocean, and in reef tanks:

Total Organic Carbon (TOC) and the Reef Aquarium: an Initial Survey, Part I

Department of Chemistry, The Pennsylvania State University, University Park, PA 16802. Ken and Kelly report on their work on Total Organic Carbon and how it relates to the reef aquarium.

reefs.com

Thus, there is about 3,000 times too little organic matter in a reef tank to cause a difference of 1 ppt in salinity measurement by refractive index.

Wow I completely believed them to, I figured a company like Hanna instruments would know what they are talking about but upon reading what you wrote about ethanol there isn’t even enough organics in our reef tanks to change the outcome of a refractometer, so meaning if they are both calibrated correctly they should technically read the same discounting there margin of error on the devices, so that leaves me with the question of witch one is right? My Milwaukee or my Hanna salinity pen? That question is difficult to answer though.

 

[Randy Holmes-Farley]

Wow I completely believed them to, I figured a company like Hanna instruments would know what they are talking about but upon reading what you wrote about ethanol there isn’t even enough organics in our reef tanks to change the outcome of a refractometer, so meaning if they are both calibrated correctly they should technically read the same discounting there margin of error on the devices, so that leaves me with the question of witch one is right? My Milwaukee or my Hanna salinity pen? That question is difficult to answer though.

There is a wonderful book called "Chemical Oceanography" by Frank Millero. It covers all things chemical in the ocean, and there's an entire chapter with a highly detailed discussion of all the way folks have measured salinity, from early approaches of drying the seawater to the latest tools oceanographers use. Conductivity is generally used the most by oceanographers, as best I can tell, but refractive index is certainly a useful tool.

No method is perfect (even drying because some chemicals are lost to the air before you can remove all water). But in general, I think most hobbyist discrepancies between salinity devices are not because the methods themselves have inherently different answers, but because the inexpensive devices and nonexpert users are not getting the most perfect answer that those methods can provide.