What is the most reliable salinity test process?

[Jan]

Hi folks,

I've been having issues with salinity measurement/management in my system.

A few weeks back I calibrated my refractometer with pinpoint calibration fluid and this showed my refractometer to be reading SW by 4 points too high. I adjusted downward and started to bring up my salinity in the tank. I also bought a Deep Six floating arm hydrometer to cross-check, and it matched exactly the readings of the newly calibrated refractometer.

So, you'd think the issue was resolved at this point, wouldn't you? Not so fast...after bringing up my tanks salinity by 5 points since three weeks ago, I am having more problems, not less.

I have 3 SPS corals dying and they have that "dry look," with empty holes where there should polyps. My fish all seem to be breathing with their mouths open, like they're having difficulty. And, I'm having trouble mixing up a batch of salt to proper salinity (1.025) without adding extra salt mix to the batch. If I just add 1/2 cup mix per gallon my mixture is turning out to be only 1.018 sg!

Having your salinity be seriously off is enough to take a tank down, I know people that it's happened to...so I'm very concerned.

How can I test my salinity and be certain that the testing tools/procedure is 100% accurate?

 

[treehugger]

that's a tough situation...i've always just used the cheap plastic hydrometers and honestly dont' really worry about it to much...i check it every couple of weeks and just dump a couple of cups in the sump if it needs to be raised otherwise I just add top off
Mine usually swings anywhere between 1.024-1.03 any given time i test it

 

[Scooterman]

What salt mix are you using?
Do you have a skimmer running?
How exactly are you mixing your salt?
How much are you evaporating each day & how are you replacing that?

Start off by taking a sample to your LFS & see what numbers they come up with & stop trying to raise it until you can grasp the problem.

 

[Jan]

Scooty,

First I heat up my RODI to temp and then add 1/2 cup salt mix per gallon of water to the mixing vat, aerate for 10-24 hours, measure salinity.

I use a 50/50 mix of salt usually.

Lately I did mix of Seachem Reef Salt + Reefers Best Salt (KZ) and came out with the low reading of 1.018.

Next batch was Seachem Reef Salt + hWMarine Mix and I added an extra cup of salt to that batch, it came out to 1.025

Batch after that was Seachem + RBS and I added the extra cup of salt, it came out to only 1.018. This is casting suspicion on the RBS salt, but I want to rule out the compounding factor of possible salinity mis-measurement before blaming the RBS salt mix.

 

[Jan]

I do have a skimmer running 24x7.

I have a J&B auto-topoff that keeps adding RODI to my system when the level gets low. My system evaporates 2-3 gallons a day depending on the weather.

 

[Scooterman]

Could it be the different salts used? I switched once & had bad results. I don't think it was the salt that shocked everything but the idea of switching that made the difference. Pick one & stick with it, for a given amount of RO/Di you should be able to get it close as to how much you need to add, say like for a 10g changes It may take you 7/8 cups, once you figure that out & is help simplify things.

 

[jezzeaepi]

Could be a bad salt mix. As much as I hate boosting the mag and calcium up to acceptable levels with IO, they have been in the game so long with such consistancy that I trust them to always be deffiecient by the same amount =P

 

[Jan]

I just got a response from Thomas Pohl himself (inventor/founder of Korallen-Zucht product line) and he said:

take exactly 38 gramms for 1L Water and you have the right salinity

So I will start by trying to confirm my salinity measuring tools, then see if I get the result that I'm supposed to with this salt.

Scooty, lots of people are mixing their salts and not having any issues so I'm doubtful that is a factor (unless there's something I completely don't understand...)

I think a bad batch of salt is a possibility as it happened a year or two ago with the RBS salt; I thought they had the problem solved or I wouldn't have bought it. I'll post my results after a quality-controlled retest

 

[OldFishMan]

Hello;

My finger taste test may be as accurate as a cheap plastic hydrometer, it does keep me from adding straight RO water :lol:

I have a cheap plastic hydrometer too. I use a refractometer; I have found the need to clean the lens and cover with RO when I recalibrate it. It has shown a couple of point deviation from salt deposits --- I calibrate mine with RO only and set it at zero. I has been right on since purchase --- I seem to drop everything but, my refractometer.

I never measure salt mix --- I just add mix until I get it right. No help on the question of a wrong mix.

A test solution sounds like a good idea though!

Enjoy!

OFM

 

[Scooterman]

At any given time, any salt manufacturer can miss a batch, it happens.
Not sure how many people actually mix batches but you have to compare apples to apples to really get those results, It was just a thought, should not be a normal practice though.
A second test from your LFS or someone else should help but really If you refract is dead on then that shouldn't be the problem. Test a sample of your pure RO/DI & see where your Refract. shows?

BTW my deep six when new was very close, even after rinsing throughly each time it slowly went adrift. I also have a refract. & a TM glass floater as back-ups.

 

[Boomer]

Jan

First Thomas Pohl does not know what he is talking about. Different salts have different moisture contents which controls the salinity from x gram used.

1000 ml - 38 = 1038 ml of water = 36. 6 ppt, as 1000 / 1038 = 3.66 % or 36. ppt. So either is math is way off or he is saying, with out saying, that there is ~ 1.5 ppt water. Thus ~36.5 - 1.5 = 35 ppt actual salinity if you add 38 grams to 1 liter of water. Well, all salts have more o water. That range is 3% -6% or 3-6 ppt. If one measures 35 grams of sea salt and adds it to 965 ml, which one would *think it would be 35 ppt as 35 grams and 965 ml of water = 1000 and 35 / 1000 = 3.5 % = 35 ppt. This does NOT happen in the real world of sea salts. 35 gram of any sea salt added to 365 ml of water will produce a actual salinity range from 28 ppt to 33 ppt depending on salt, do to moisture content.

Point 2 and question as it was not given. Your raised the salinity 5 ppt. How long did it take to do this ? It should have taken 5 day at 1 ppt / day and no more. . If you did it all at once, that is an absolute No-No and is why you are having animal issues.

If you cal the refract and the Deep Six is the same more than likely that is what the salinity is. As Scoot has pointed out a TM hydrometer is the best back up, as it will NOT be off. There is still *chance that the cal solution was off and the Deep Six reading being the same is a coincidence but I doubt it.

Mixing salts of x with y is not an issue

 

[roscoe]

I use reef crystals salt. I do a 10g water change every week. Every time I mix the salt following their direction at half a cup per/g I always end up at 1.022-1.023. So I started to add an extra 1/2 cup to the 10g mix for a total of 5 1/2 cups and the salinity always hit right at 1.026. That is what I figured that it needs, to get the salinity to be where I wanted.

 

[Jan]

Jan

First Thomas Pohl does not know what he is talking about. Different salts have different moisture contents which controls the salinity from x gram used.

1000 ml - 38 = 1038 ml of water = 36. 6 ppt, as 1000 / 1038 = 3.66 % or 36. ppt. So either is math is way off or he is saying, with out saying, that there is ~ 1.5 ppt water. Thus ~36.5 - 1.5 = 35 ppt actual salinity if you add 38 grams to 1 liter of water. Well, all salts have more o water. That range is 3% -6% or 3-6 ppt. If one measures 35 grams of sea salt and adds it to 965 ml, which one would *think it would be 35 ppt as 35 grams and 965 ml of water = 1000 and 35 / 1000 = 3.5 % = 35 ppt. This does NOT happen in the real world of sea salts. 35 gram of any sea salt added to 365 ml of water will produce a actual salinity range from 28 ppt to 33 ppt depending on salt, do to moisture content.

Point 2 and question as it was not given. Your raised the salinity 5 ppt. How long did it take to do this ? It should have taken 5 day at 1 ppt / day and no more. . If you did it all at once, that is an absolute No-No and is why you are having animal issues.

If you cal the refract and the Deep Six is the same more than likely that is what the salinity is. As Scoot has pointed out a TM hydrometer is the best back up, as it will NOT be off. There is still *chance that the cal solution was off and the Deep Six reading being the same is a coincidence but I doubt it.

Mixing salts of x with y is not an issue

Hi Boomer

T. Pohl was talking about the proper mixing of the KZ "Reefer's Best Salt," not any other salt. He said this to me because I started a thread on the Zeovit forum stating that when I mixed up the RBS salt with the same proportions I've always used with other salts (1/2 c mix to 1g water), I was coming out with very low salinity SW--1.018. I still have to complete my testing of his mix proportions but it appears that a 15 gallon batch of SW will require 9 cups of RBS instead of the 7.5 cups I am used to throwing in.

As for how long I took to raise my salinity by 5 points. I did this over ~12 days. I raised it 3 points in 5 days, then kept it the same for a couple days, then slowly raised it the other 2 points and kept it there. I am currently at 1.023. The odd part for me is that I have several SPS corals that are now dissolving and/or have burnt tips. These corals were looking good-to-awesome with the very low salinty and now are toast. I am questioning the RBS itself, as I just recently started using it about a month ago.

 

[Boomer]

Ok then for what Phol said, kinda, maybe, see below.

when I mixed up the RBS salt with the same proportions I've always used with other salts (1/2 c mix to 1g water), I was coming out with very low salinity SW--1.018.

This makes no sense at all they should be nowhere near 1.018 = 24 ppt. Unless the salt is not dissolving or is a really bad batch of low salinity and I have never herd of such a thing. The lowest salinity salt mixes is ~ 29 ppt. If you have to use 9 cups of RBS vs 7.5 of others, then that RBS must be loaded with water and does not conform at all to Phol 's claim.

But lets fix you up

Take some of each salt, RBS, RC, SeaChem, etc., and RO/DI water to the local drug store. Tell him to weigh out 35 grams of each and dissolve it in 965 ml of RO/DI water. When you get home then test each for salinity. Also have him weigh out a cup of each, using your cup. A full cup is fill to overfull and plow off with the back side of a knife. No tapping the cup on table to get more in the cup. From these you will be able to determine how much to use of either to get X Salinity.

 

[Jan]

Boomer, that is a very good idea for testing.

Related question...is it possible for a box of salt to "settle" somehow, so that certain elements/ions fall to the bottom of the container, resulting in the top portion mixing at a lower salinity than the same volume of mix from the bottom of the container? I wondered about this. If it is possible, then this may explain why some of my corals have not been happy with recent water changes...they may be getting too much of something else within the mix.

I do agree that this particular box of salt has quite a bit of moisture in it and is pretty compacted, making it a little more difficult to mix up within the box.

 

[Scooterman]

I had some IO a while back clump up like rock, LOL
I still used it after smashing it throughly & removing what didn't dissolve!

 

[Boomer]

Yes, Jan salts do settle, usually do to density and grain size. Heavier grains sink more than lighter grains. And bigger grains go to top and smaller grains go to the bottom ( no this is not a typo error and is called "The Brazilian Nut Theory" ) These are why we try to tell people to mix the bag well before use. However, it will usually never get to what you got. It is usually that the ions in your salt mix will not be about the same ratios from batch to batch. Allot of moisture is the sign of a poor salt or a bag that has let in to much moisture but is usually still fine to use.

 

[Jan]

Hi everybody, hope y'all had a good holiday weekend.

Question about calibrating a refractometer. From what I've read, the procedure is to calibrate with both RO/DI and a solution like pinpoint (@35ppm or 1.0264 salinity IIRC)

What does it mean when the pinpoint solution shows exactly where it should be, at the 35 ppm or ppt...but the RODI does't come in at 0, instead it reads a few ml below the 0 point? Does that mean anything? A funky slope in the refractometer or anything? The reason I'm asking is that I've heard of people whose refractometers were way off even after calibrating.

And I'm still having to add a fair amount more salt mix than I think I should in order to make a batch of SW at 1.025 (like 15 cups of salt to 25 g. of RODI)
FWIW, my cheap-o swing arm still matches my refractometer....and I'm using different salt now, not the suspect Reefer's Best.

 

[Scooterman]

I'd trust the pinpoint solution over ro/di.

It sounds to me you may had a problem with the salt.
maybe go buy a small bag & make up some of that & compare the results?

 

[Jan]

I'd trust the pinpoint solution over ro/di.

It sounds to me you may had a problem with the salt.
maybe go buy a small bag & make up some of that & compare the results?

Actually, the article I read said that the procedure is to calibrate with both RODI and pinpoint and that both should be correct. But slope irregularities can make one or the other reading be off...