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Salinity and mixing


MrZ2u

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Neub here...using red sea pro and shooting for the numbers on the bucket. I weighed out the exact weight of salt in grams and water with a pyrex measuring pitcher. Measured with a refractometer a couple minutes after mixing and its higher than the bucket says it should be. Does it need to sit a while to show the final gravity?

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I mixed three gallons. It says 1.5lb for 5gal. I converted to grams and calculated 136gr per gallon. I have a food grade mixing bucket I got from Ace Mart that I made 1, 1.5 and 2 gal graduated marks with a 32oz pyrex mixing pitcher. I may go back and make it by weight to be sure I am accurate on the water marks. I am also going to see if I can test my refractometer at RiverCity against theirs to be sure its accurate, though I do have the calibration liquid and mine is zeroed accurately according to the directions. The water in the tank is about 3/4 premix from River City and its almost the same. I had it in a bucket with the rock and topped it off with RO twice over the week I have had the rock. The remaining .25% was fresh mix at the 136gr/gal ratio. Consistency is what I am shooting for here really. As long as I can adjust for whatever error, if any, there is then I should be good to go. Still in the establishing SOP phase so nothing urgent really...just learning the numbers.

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Man, that sounds like one of the frustrating parts of doing a small tank. I mix in ~15gal batches and purposefully go low on my salt on the 1st dump, knowing that I am going to add more the next day. That seems like it could offend your precision sensibilities, but maybe go that direction until you find that exact salt weight for your 3gal mix?

And maybe it isn't really 24hrs for me....I turn my RODI on at night right before bed and it's usually filled when I wake up. Add salt, go to work, check in the evening, adjust and then check occasionally. Usually start the process on a Thurs for a Sat water change.

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I'm not sure if you're testing anything besides sg, but there is normally a discrepancy between the label and the tests. I've seen some people have done analysis on the different salt mixes in the past. Some of it boiled down to separation of the granules during shipment. Heating the water will help to get a consistent reading. It also helps to put a pump in the water an hour before mixing.

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I always under mixed and then add more salt to get up to the correct sg. You could obviously do the opposite, but basically need to mix in a large enough container that you are mixing a smaller percentage of it and then add RO to get down to the correct sg. I've never seen a salt that is perfectly consistent for g to v of specific sg/salinity. Also, make sure you are calibrating your refractometer with a 1.026 solution. There can be quite a lot of error calibrating to zero.

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I always under mixed and then add more salt to get up to the correct sg. You could obviously do the opposite, but basically need to mix in a large enough container that you are mixing a smaller percentage of it and then add RO to get down to the correct sg. I've never seen a salt that is perfectly consistent for g to v of specific sg/salinity. Also, make sure you are calibrating your refractometer with a 1.026 solution. There can be quite a lot of error calibrating to zero.

Zeroed was a bad word choice...I calibrated with this https://www.amazon.com/Standard-Seawater-Refractometer-Calibration-Solution/dp/B0053DSWJA so not to zero.

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I always under mixed and then add more salt to get up to the correct sg. You could obviously do the opposite, but basically need to mix in a large enough container that you are mixing a smaller percentage of it and then add RO to get down to the correct sg. I've never seen a salt that is perfectly consistent for g to v of specific sg/salinity. Also, make sure you are calibrating your refractometer with a 1.026 solution. There can be quite a lot of error calibrating to zero.

Zeroed was a bad word choice...I calibrated with this https://www.amazon.com/Standard-Seawater-Refractometer-Calibration-Solution/dp/B0053DSWJA so not to zero.

Good deal. I've been using that same stuff for a long time. Just saw the zero'd comment and assumed you were using a 0ppm or RO to calibrate, which is better than nothing, but can definitely be skewed when needing a higher target salinity.

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Has anyone noticed a difference between calibrating with solution versus RODI? My refractometer instructions say to use RODI. I've had it verified twice a year since 2013 at RCA.

I haven't used RO for calibration in a few years, but I think mine was off a hair compared to calibrating at 1.026. Check out this section on the reefkeeping article. It's mainly due to calibrating at zero essentially can magnify imperfect refractometer precision. http://reefkeeping.com/issues/2006-12/rhf/#11

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Has anyone noticed a difference between calibrating with solution versus RODI? My refractometer instructions say to use RODI. I've had it verified twice a year since 2013 at RCA.

Given how cheap a bottle of the solution is and how long it should last I'd say its kind of a no brainer. River City has it for $9.99 so you dont even have to wait on shipping :)

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1 cup salt per 2 gallons RO is the magic measurement. (dry measure scoop, flat..not heaping.) works with red sea pro and instant ocean reef.

Sent from my SM-G920P using Tapatalk

This! My exact measurement too. If you go by the gram thing it's way low. IMO

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In my measuring I did find using level 1/4 cups on the scale was by grams with in 5 of the mark at 1 cup. I suppose both can be a benchmark that could be off one way or the other depending on moisture level in the salt.

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Has anyone noticed a difference between calibrating with solution versus RODI? My refractometer instructions say to use RODI. I've had it verified twice a year since 2013 at RCA.

I haven't used RO for calibration in a few years, but I think mine was off a hair compared to calibrating at 1.026. Check out this section on the reefkeeping article. It's mainly due to calibrating at zero essentially can magnify imperfect refractometer precision. http://reefkeeping.com/issues/2006-12/rhf/#11

Its more the device's accuracy than the calibration solution. So if you calibrate the device closer to the actual number (1.026 or 35ppm)that you will vbe using it at then you should have less of a variation error

1 cup salt per 2 gallons RO is the magic measurement. (dry measure scoop, flat..not heaping.) works with red sea pro and instant ocean reef.

Sent from my SM-G920P using Tapatalk

Not sure what ppm you are trying to hit but I have always shot for 35ppm or 1.026 SP. I always use 3 cups salt to 5 gals RODI to get to these numbers. Which is0.6 cups per gallon where you are quoting 0.5 cups per gallon

I mixed three gallons. It says 1.5lb for 5gal. I converted to grams and calculated 136gr per gallon. I have a food grade mixing bucket I got from Ace Mart that I made 1, 1.5 and 2 gal graduated marks with a 32oz pyrex mixing pitcher. I may go back and make it by weight to be sure I am accurate on the water marks. I am also going to see if I can test my refractometer at RiverCity against theirs to be sure its accurate, though I do have the calibration liquid and mine is zeroed accurately according to the directions. The water in the tank is about 3/4 premix from River City and its almost the same. I had it in a bucket with the rock and topped it off with RO twice over the week I have had the rock. The remaining .25% was fresh mix at the 136gr/gal ratio. Consistency is what I am shooting for here really. As long as I can adjust for whatever error, if any, there is then I should be good to go. Still in the establishing SOP phase so nothing urgent really...just learning the numbers.

I find the easiest way to mix is in five gallon batches of RODI. and add 3 level cups of salt and mix and heat to 80 degrees for one hour and let set one hour. Then test with a calibrated refractometer, and I calibrate every time I use mine with a known 35ppm solution like RCA sells If it is a little low I add 3 tablespoons at a time but usually is spot on. Be sure to accurately measure out five gallons on your bucket and fill to this point. ~ 1.75 " from the top. A 5 gal bucket filled to tippy top usually holds ~ 5.86 gals. and this is where one usually gets variation in their ppm per 3 cups salt per 5 gal RODI.

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remember, all theses measurements are assuming 25Celcius (77F) water. My 1c=2g works for 78-78.5 smile.png probably shoulda mentioned that in my original post, itll be updated smile.png

It is true that salts have retrograde solubility and this means it is more soluble at colder temps and higher pressures meaning if you overheat the water and mix then when it cools to say room temp precipitation of calcium carbonate.can occur. But I have never had this trouble at 80 degrees. It is fine to mix at lower temps for sure even all the way down to 72F. But it takes a whole lot longer to mix clear at these lower temps. Maybe 77 is the perfectly safe number bnt as long as you do not generate precipitate then it will not change your salinity level by mixing at slightly different temps.

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Just throwing in my 2 cents. I pretty much always mix salt to a lower salinity than the system I'm adding it too. By how much I can't say as it's pretty rare to actually test the new saltwater. But depending on the salinity of the system I'm adding it too it can be pretty weak. I also typically mix it just minutes before using. Instant Ocean usually clears up pretty quick when mixed. As far as calibrating refractometers I only use the ones that read all the way to zero SG/PPT and can't tell the difference between tapwater or RO water or RO/DI for zeroing it. If someone is using one of the types that only reads a narrow range of salinity obviously the correct standard calibrating fluid should be used. As far as acceptable range of change I haven't seen any noticable reaction by corals to a 10% change in salinity. (Sprung actually suggests a doing a sudden 10% change in salinity with a water change to help control "ick".)

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it was not a comment of solubility, but the fact that you have to factor in temperature when measuring salinity.

Aren't most current age refractometers temperature compensating (ATC)?

This correct the same water tested at 77 F and then heated to 80 F should and would have the same SG or ppm of salt. You just need to utilize the self compensating refractometer and wait for the solution applied to reach the temperature of the meter before reading it. This simply put means put a couple of drops on the slide and wait 3-5 minutes before reading.

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