High Tide Aquatics

Red Sea salt mixed to 6dkh

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richiev

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I'm sure this is a vote for mixing salt bags together well, but a quick anecdote... My DIY automated alk tester is working well, but I've been testing over and over as I get confidence in it. Currently I have it filling from a cup then dumping into a bucket, because I don't yet trust it to put the waste water into the tank.

I grab a cup of water from the tank, pour a cup of new saltwater into the tank, then measure that cup of tank water. I've been noticing my alk readings seem to be quickly dropping, and I therefore keep testing to verify it's consistent. Every time I compare it to my Hanna I get matching numbers though, so I was very confused. I then decided to test my fresh mixed water I've been using.

Turns out my tester is working correctly, and my fresh mixed water has an alk of 6.0. Standard black bag. I'm using the last of the bag.

Very surprised, and this may explain some of the weirdness I've been having recently. At least my auto tester is working well though.

I'm going to mix the rest of the salt I have with another bag and mix that salt around more. I've got 15gal of fresh saltwater I'm going to need to add alk to to try and get it up to 8.0 again.

Not a huge deal, but annoying.
 
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Coral reefer said:
Is it fresh mixed or has been sitting awhile?
Sure the salinity is accurate?
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Just mixed yesterday. Salinity is for sure accurate. I didn't go in and recalibrate my Hanna today, but I'm getting the same salinity in my tanks as the water mixing station.
Matthew Meyer said:
I make saltwater about a week ahead of time. Does that change the chemistry. I do heat it up and mix it for about an hour day of.
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BRS actually did a test on this. The video is about how long ahead of time should you mix saltwater. It was informative, including them pointing out that unless you want to precipitate stuff out, in mixes like Red Sea's your supposed to mix at something like 60-70°F and after an hour+ then you can warm it to proper temp. The BRS test looked at Alkalinity, and showed how stored water drops in Alk over time, eventually reaching a stable point. I'm not sure I really buy that entirely, but the premise that it drops over time naturally makes sense.

Alkalinity is the ability of water to absorb acid while minimizing pH movement. Add acid, alkalinity drops. Add more acid, alkalinity drops more. If you leave water out, it's going to absorb some amount of CO2, making carbonic acid, which'll get absorbed by the alkalinity and then drop it. Repeat over time. At least, that's what seems reasonable.

From a quick google:

> The pH of pure water (H20) is 7 at 25 °C, but when exposed to the carbon dioxide in the atmosphere this equilibrium results in a pH of approximately 5.2 because CO2 in the air dissolves in the water and forms carbonic acid.

So presumably as long as your pH is above 5.2, your water is slowly consuming Alkalinity.

I'm sure a chemist up in here can speak more authoritatively on this though.
 
Also note to self, be less aggressive when adding Alk to mixed saltwater. I just shot my mixed water to 11dkh and now have to mix more to dilute it, plus adding some HCL to drop it additionally. I'll then have to try and raise the pH again by bubbling it. Ooops.
 
Are you using the standard blue bucket or coral pro black bucket? Red Sea announced in January they reformulated their salt. Do you know if your salt is before or after the reformulation? Regardless 6 dKH is significantly off from their advertised parameters.
 
richiev said:
Just mixed yesterday. Salinity is for sure accurate. I didn't go in and recalibrate my Hanna today, but I'm getting the same salinity in my tanks as the water mixing station.

BRS actually did a test on this. The video is about how long ahead of time should you mix saltwater. It was informative, including them pointing out that unless you want to precipitate stuff out, in mixes like Red Sea's your supposed to mix at something like 60-70°F and after an hour+ then you can warm it to proper temp. The BRS test looked at Alkalinity, and showed how stored water drops in Alk over time, eventually reaching a stable point. I'm not sure I really buy that entirely, but the premise that it drops over time naturally makes sense.

Alkalinity is the ability of water to absorb acid while minimizing pH movement. Add acid, alkalinity drops. Add more acid, alkalinity drops more. If you leave water out, it's going to absorb some amount of CO2, making carbonic acid, which'll get absorbed by the alkalinity and then drop it. Repeat over time. At least, that's what seems reasonable.

From a quick google:

> The pH of pure water (H20) is 7 at 25 °C, but when exposed to the carbon dioxide in the atmosphere this equilibrium results in a pH of approximately 5.2 because CO2 in the air dissolves in the water and forms carbonic acid.

So presumably as long as your pH is above 5.2, your water is slowly consuming Alkalinity.

I'm sure a chemist up in here can speak more authoritatively on this though.
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The above pH vs CO2 discussion is correct for pure water, which isn’t what we are using in our tanks. Our reef tank water is heavily buffered with organic buffers, but the most important is carbonate. This is also what we mean by alkalinity, the ability to buffer against pH change with acid addition. People talk about alkalinity as a measure of carbonate, but it really is a measure of acid buffering ability.

With standard sample reef tank parameters (salinity 35 ppt, alkalinity 8.3 dKH, 80F) and outdoor air (CO2= 420 ppm), the pH is about 8.3 at equilibrium. See below screenshot from hamzasreef.com

1681273738885.jpeg



Note that CO2 in air used to be about 320 ppm in 1970 and now is 420 ppm.

1681273992340.png


Also note that your estimate of the equilibrium pH of 5.2 is about 1000 times more acidic than the true equilibrium pH of 8.3. Buffers matter.
 
JVU said:
The above pH vs CO2 discussion is correct for pure water, which isn’t what we are using in our tanks. Our reef tank water is heavily buffered with organic buffers, but the most important is carbonate. This is also what we mean by alkalinity, the ability to buffer against pH change with acid addition. People talk about alkalinity as a measure of carbonate, but it really is a measure of acid buffering ability.

With standard sample reef tank parameters (salinity 35 ppt, alkalinity 8.3 dKH, 80F) and outdoor air (CO2= 420 ppm), the pH is about 8.3 at equilibrium. See below screenshot from hamzasreef.com

View attachment 46745


Note that CO2 in air used to be about 320 ppm in 1970 and now is 420 ppm.

View attachment 46746

Also note that your estimate of the equilibrium pH of 5.2 is about 1000 times more acidic than the true equilibrium pH of 8.3. Buffers matter.
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Great charts and info! You've made me realize there's some underlying things I don't really understand in the alkalinity + CO2 area. The first one is why changing CO2 levels in your house, lead to up swings in your aquarium. I can understand why increases in CO2 decrease pH, but I'm not clear why when CO2 is lowered pH increases again versus staying down. Presumably the CO2 decides to detach and go back dissolved and then off gas into the atmosphere instead of staying attached to the H molecule?

Secondly I'm not clear if similarly the Alk (CO3?) gets "used" by the CO2 (carbonic acid) or if it's temporarily used, and then if the CO2 off gases if the Alk similarly gets freed back up to be reusable again later. I'd always assumed it's permanently used, barring you evaporating it all and baking it or something (what people do to convert baking soda).

However if it's permanently used, then I don't understand why alk wouldn't be constantly slowly dropping in tanks. Unless it is constantly slowly dropping and at don't discuss that.

Any pointers on that?
SupraSaltyReefer said:
Are you using the standard blue bucket or coral pro black bucket? Red Sea announced in January they reformulated their salt. Do you know if your salt is before or after the reformulation? Regardless 6 dKH is significantly off from their advertised parameters.
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I'm using the black bags: https://www.bulkreefsupply.com/aquarium-salt-mix-red-sea.html which I pour into a red sea bucket after opening. I've had this bag for quite awhile.

I can't say if the rest of this bag was that way, or if I'm just getting unlucky and the bottom of the bucket had something weird going on. I think I'd of noticed if it was this far off before, but I also didn't have an automated tester until recently and I've been having issues with sps for a bit.
 
richiev said:
Great charts and info! You've made me realize there's some underlying things I don't really understand in the alkalinity + CO2 area. The first one is why changing CO2 levels in your house, lead to up swings in your aquarium. I can understand why increases in CO2 decrease pH, but I'm not clear why when CO2 is lowered pH increases again versus staying down. Presumably the CO2 decides to detach and go back dissolved and then off gas into the atmosphere instead of staying attached to the H molecule?

Secondly I'm not clear if similarly the Alk (CO3?) gets "used" by the CO2 (carbonic acid) or if it's temporarily used, and then if the CO2 off gases if the Alk similarly gets freed back up to be reusable again later. I'd always assumed it's permanently used, barring you evaporating it all and baking it or something (what people do to convert baking soda).

However if it's permanently used, then I don't understand why alk wouldn't be constantly slowly dropping in tanks. Unless it is constantly slowly dropping and at don't discuss that.

Any pointers on that?

I'm using the black bags: https://www.bulkreefsupply.com/aquarium-salt-mix-red-sea.html which I pour into a red sea bucket after opening. I've had this bag for quite awhile.

I can't say if the rest of this bag was that way, or if I'm just getting unlucky and the bottom of the bucket had something weird going on. I think I'd of noticed if it was this far off before, but I also didn't have an automated tester until recently and I've been having issues with sps for a bit.
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Alkalinity isn’t really “used up” in the normal course of buffering pH swings against acid. If you add acid (or add CO2 like with respiration), then add base (or remove CO2 like with photosynthesis), the carbonate is buffering against those changes wildly swinging the pH as much as they would without the buffer, but not being used up in a real sense. None of these changes are irreversible like it sounds like you are considering. The entire carbonate system is in a dynamic equilibrium, which is to say if you add more of one thing you can push the following equation the other direction (from Randy Holmes-Farley’s article on Photosynthesis and the Reef Aquarium: Carbon Sources):

1681279086963.jpeg


H+ here is acidity, and lower pH is defined as more H+. Notice all of these arrows are double arrows, so each reaction goes either direction. So if you add CO2, it combines with water to form carbonic acid. The reason this is acidic is because when some of it spontaneously dissociates into bicarbonate, it releases H+ (acidity). Some of this bicarbonate can spontaneously dissociate into carbonate, releasing more H+. So if you add CO2 (ie metabolism in the tank or mouth breathers around your tank) you push the reaction to the right (more acidic) and if you use up CO2 (ie photosynthesis or CO2 scrubber or outside air) you push the reaction to the left (less acidic). In any case you aren’t really using up the buffer. The normal swings we see in pH every day are due to the daily swings of metabolism vs photosynthesis mostly.

Carbonate does get ”used up” when it precipitates out of solution as calcium carbonate, either in a coral or on a pump (for example). The supersaturated salt mixes that give you artificially high dKH that you would never see on a reef often have this precipitation on surfaces the longer you let it sit in the bin before use, which is why you see the alkalinity drop over time. The more naturally buffered salt mixes around 7-8 dKH don’t generally have this issue as much.
 
You said black bucket but you linked to blue bucket. The black bucket Red Sea salt has the artificially elevated alkalinity I was talking about isn’t very stable in solution.
 
JVU said:
You said black bucket but you linked to blue bucket. The black bucket Red Sea salt has the artificially elevated alkalinity I was talking about isn’t very stable in solution.
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I believe he’s referring to this sack which is the blue bucket salt at 8dKH. It’s dark blue so looks black in the picture. Versus the Coral Pro is the Red sack which is12 dKH and normally in a black bucket. Confusing. Lol.

FA52EC8E-09C6-4243-95BC-F35829B41DCB.jpeg
076E1B9C-150D-48B7-BD3F-A4D7D668C09B.jpeg
 
SupraSaltyReefer said:
I believe he’s referring to this sack which is the blue bucket salt at 8dKH. It’s dark blue so looks black in the picture. Versus the Coral Pro is the Red sack which is12 dKH and normally in a black bucket. Confusing. Lol.

View attachment 46748View attachment 46749
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Yeah, that stuff. Bag is "black", bucket version is "blue". I used to use the red but switched sometime last year since I don't like to keep my alk as high as red mixes.
 
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