Not sure why I need to add more IO than expected

[NormanB]

So, the instructions on the bucket says 1.5 pounds per 5 gallons to mix to 1.022. The conversion calculator converts this to 29.2 PPT. Starting with this + 20% get you to 35 PPT, which is where I want to be.

1.5 # is about 680.4g then +20% = 816.5g Thus, 816.5g in 5 gal should = 35 PPT.

However, I add 850g in 5 gal to get to 35 PPT, thus my question, why do I need an additional 33.5g of IO to get to 35 PPT?

I realize temperature has an impact here so maybe that is the issue?

More info: typically the water just prior to mixing is about 73F and rises to about 75F by the next day when I test for salinity and normally get close to or right at 35 PPT.

Tank temp is set to 78F and varies a bit as expected.

Salinity is checked with a Hanna salinity checker which is recalibrated each month as recommended by Hanna.

RODI is used in the makeup and has 0 TDS.

Any ideas here? Or am I missing something, or miscalculated my numbers?

Thanks so much

 

[Reefer Matt]

So, the instructions on the bucket says 1.5 pounds per 5 gallons to mix to 1.022. The conversion calculator converts this to 29.2 PPT. Starting with this + 20% get you to 35 PPT, which is where I want to be.

1.5 # is about 680.4g then +20% = 816.5g Thus, 816.5g in 5 gal should = 35 PPT.

However, I add 850g in 5 gal to get to 35 PPT, thus my question, why do I need an additional 33.5g of IO to get to 35 PPT?

I realize temperature has an impact here so maybe that is the issue?

More info: typically the water just prior to mixing is about 73F and rises to about 75F by the next day when I test for salinity and normally get close to or right at 35 PPT.

Tank temp is set to 78F and varies a bit as expected.

Salinity is checked with a Hanna salinity checker which is recalibrated each month as recommended by Hanna.

RODI is used in the makeup and has 0 TDS.

Any ideas here? Or am I missing something, or miscalculated my numbers?

Thanks so much

I find the instructions get you close, but figuring out the precise amount of salt to mix takes some trial and error. I have a popcorn cup, and I know 5 of those gets me to 1.025 salinity in 30 gallons. I don't have to measure or weigh anything additional, it is there everytime. It is possible the batch is different, or not homogenized as well.

 

[chipmunkofdoom2]

An extra 33.5g is less than 4% more than your original calculations. That could easily be measurement error, on either the scale or the salinity side. Or, it could be moisture in the salt mix. I wouldn't worry about it.

 

[Jekyl]

Just to be sure... these measurements are done with a refractometer, dialed in with calibration liquid, right?

 

[14 foot reef]

@jda ....... I think this forum member has an exact process and dosage measument he has been doing with Instant Ocean for many many years. Lets see if he's around to chime in.

 

[Randy Holmes-Farley]

How are you measuring salinity? maybe it is not accurate.

 

[NormanB]

An extra 33.5g is less than 4% more than your original calculations. That could easily be measurement error, on either the scale or the salinity side. Or, it could be moisture in the salt mix. I wouldn't worry about it.

Sounds good. I guess my OCD came out!

 

[NormanB]

Salinity measurements are made with a Hanna salinity checker which is calibrated monthly per Hanna instructions.