Please help me understand these surprise salinity readings.

[Dom]

Currently, I am setting up two temporary tanks which will house the contents of my main display, so that I can drain and relocate the tank to different wall of the room.

The two temporary tanks are a 40 gallon and a 10 gallon. Currently sitting at 76 degrees, I added one pound of IORC. After 12 hours, I tested salinity.

My results:

The 40 gallon tank has a reading of 5ppt at 76 degrees.
The 10 gallon tank has a reading of 10ppt at 76 degrees.

Since the 10 gallon tank is 25% of the volume of the 40 gallon, and since the same amount of salt was added to both tanks, it makes sense to me that the salinity in the 10 gallon should be 4 times that of the 40 gallon, or 20ppt. It isn't.

Thoughts?

Thank you,
Dom

 

[vaguelyreeflike]

One pound of salt for 50 gals is nothing, which is why the salinity is so low. Typically you need closer to 14-16lb of salt for 50 gals of 0ppt water, but this can vary. I always pre-mix my salt and test until it’s at the desired level before adding to the tank.

 

[Dom]

One pound of salt for 50 gals is nothing, which is why the salinity is so low. Typically you need closer to 14-16lb of salt for 50 gals of 0ppt water, but this can vary. I always pre-mix my salt and test until it’s at the desired level before adding to the tank.

2 tanks.

Tank A is 25% of the total capacity of tank B. When adding 1 pound of salt to each, tank A's salinity level should be 4 times that of tank B.

It isn't. I'm trying to understand why.

 

[Dom]

@Randy Holmes-Farley

 

[Ben's Pico Reefing]

How many actual gallons are in each tank? Size of tank doesn't mean how much you filled total volume of liquid. You would need to measure the water added as well to ensure what total volume of water you are using. Also with more surface area the more evaporation so depends on time between mixing. Also has any salt settled on bottom or not fully mixed?

 

[Randy Holmes-Farley]

How are you measuring salinity?

 

[vaguelyreeflike]

2 tanks.

Tank A is 25% of the total capacity of tank B. When adding 1 pound of salt to each, tank A's salinity level should be 4 times that of tank B.

It isn't. I'm trying to understand why.

I see what you mean now, I thought you were wondering why it wasn’t full salinity, my bad.

That is odd, possibly variation among the salt itself?

 

[Dom]

How are you measuring salinity?

I'm using a freshly calibrated refractometer.

I tested and received the mentioned results. I calibrated and tested again. Same result.

 

[Dom]

I see what you mean now, I thought you were wondering why it wasn’t full salinity, my bad.

That is odd, possibly variation among the salt itself?

I thought testing error. But I re-calibrated the refractometer and tested again with the same results.

 

[vaguelyreeflike]

I thought testing error. But I re-calibrated the refractometer and tested again with the same results.

That’s why I wonder if the salt has variation in it such as higher or lower levels of sodium vs other ‘salts’ such as magnesium, one scoop from one part of the bucket may have yielded different results from another.

Are you also using a calibrated/tested scale to weigh the salt out?

 

[Dom]

That’s why I wonder if the salt has variation in it such as higher or lower levels of sodium vs other ‘salts’ such as magnesium, one scoop from one part of the bucket may have yielded different results from another.

Are you also using a calibrated/tested scale to weigh the salt out?

It’s the same salt from the same bag.

After adding 1 pound of salt to each tank from the same bag, the 10 gallon tank should have 4 times as much salinity, regardless if the scale is calibrated or not.

 

[Ben's Pico Reefing]

How did you measure the water? And what is the exact amount of water you added?

 

[Dom]

How did you measure the water? And what is the exact amount of water you added?

It is a 10 gallon tank and a 40 gallon tank. I didn't physically measure the amount of water in each. I have no reason to believe these tanks are more or less than the advertised capacity.

 

[drolmaeye]

I am fairy certain that IORC (as well as any other brand of salt) is relatively uniform. If this is the case, then there must be a misunderstanding in one of more factors including how much water is in the tanks (e.g., is there sand or rock? how close to the top is it filled?), how much salt was added to the tanks, how completely the salt was mixed/dissolved. I have never added salt directly to a tank, but instead have always mixed separately, measured salinity, and then moved to tank, so I don't have a good feeling for which of these factors may be the biggest culprit.

For the salt I use, and the volumes and salinities you mentioned, I would need to add almost exactly 2 lbs of salt to get 40 gallons up to 5 ppt, and almost exactly 1 lb of salt to get 10 gallons up to 10 ppt.

 

[Hubert J. Farnsworth]

couple things. my 20 gallon long holds closer to 17 gallons of water than 20.

how well are you mixing the water in the tank? i recommend using continuously circulating pumps for an hour or more.

if the water isn't mixed well enough, you could have different layers of salinity at different depths. the water on the bottom will have a higher salinity than the water on the top if this is the case.

 

[Ben's Pico Reefing]

So a container or tank is list to hold 10 gallons. Unless you fill them all the way. You truly do not have 10 gallons of water. Same with 40 gallon but mostly more than 40

Standard 10 gallon tank is 10.389 gallons of total volume
Standard 40 gallon breeder tank is 44.88 gallons of total volume

Edit: I'm also assuming there is no equipment or anything displacing the water in the tank as well.

If only 9 gallons are filled and 43 gallons in other. You will get your 20 percent.

 

[Dom]

I am fairy certain that IORC (as well as any other brand of salt) is relatively uniform. If this is the case, then there must be a misunderstanding in one of more factors including how much water is in the tanks (e.g., is there sand or rock? how close to the top is it filled?), how much salt was added to the tanks, how completely the salt was mixed/dissolved. I have never added salt directly to a tank, but instead have always mixed separately, measured salinity, and then moved to tank, so I don't have a good feeling for which of these factors may be the biggest culprit.

For the salt I use, and the volumes and salinities you mentioned, I would need to add almost exactly 2 lbs of salt to get 40 gallons up to 5 ppt, and almost exactly 1 lb of salt to get 10 gallons up to 10 ppt.

These are two temporary tanks. They are bare bottom. For the purpose of my post, the tanks have 10 gallons and 40 gallons.

Again, I added 1 pound to each tank and received the posted results.

Since posting, I've added another pound to each. My expectation:

The 40 gallon tank will double to 10ppt and the 10 gallon will double to 20ppt.

There is nothing wrong with adding salt directly to a new tank. Mixing outside the tank is something you do for a water change. A person who owns a 500 gallon tank doesn't mix in a 500 gallon container and then pump it into the tank. They mix directly in the tank.

 

[Dom]

This is a math question.

Tank A holds 25% of the capacity of tank B.

If both tanks receive the same quantity of salt, tank A salinity should be 4 times greater than tank B.

Am I looking at this wrong?

 

[Randy Holmes-Farley]

I don’t actually know how good typical refractometers are at very low salinity.

The Milwaukee digital only claims +/- 2 ppt.

If the measurements are at low ppt values, these errors can become large fractions of the total.

 

[Randy Holmes-Farley]

This is a math question.

Tank A holds 25% of the capacity of tank B.

If both tanks receive the same quantity of salt, tank A salinity should be 4 times greater than tank B.

Am I looking at this wrong?

Yes, it is simple math, but then applied to devices that may not be super accurate.