Salt Mixing with Low DKH Question...

[Aaron Shapiro]

I've noticed since setting up my trident that my Alk typically drops after water changes -- this seems odd to me because I've recently switched from Tropic Marin to Fritz RPM which should be between 8-9 dkh and my tank has always been in the low 7's. So tonight I mixed up 5g of water to 35ppm (calibrated refractometer) and tested it. And it was LOW like 5.8-6dkh...

Is there something with mixing saltwater that can precipitate out the alkalinity? My Tropic Marin salt was always low too... I've never really been able to get my dkh up to 8-9 where I want it.

I'm starting to think maybe it's me, not the salts... I dosed my water change water up to the DKH I desired with BRS 2-part, but this seems less sustainable than just using a salt that mixes correctly.

 

[anthonygf]

I've noticed since setting up my trident that my Alk typically drops after water changes -- this seems odd to me because I've recently switched from Tropic Marin to Fritz RPM which should be between 8-9 dkh and my tank has always been in the low 7's. So tonight I mixed up 5g of water to 35ppm (calibrated refractometer) and tested it. And it was LOW like 5.8-6dkh...

Is there something with mixing saltwater that can precipitate out the alkalinity? My Tropic Marin salt was always low too... I've never really been able to get my dkh up to 8-9 where I want it.

I'm starting to think maybe it's me, not the salts... I dosed my water change water up to the DKH I desired with BRS 2-part, but this seems less sustainable than just using a salt that mixes correctly.

I just switched salt from RC to Fritz my first 5 gallon batch the DKH was up to 11.

 

[Dilan Patel]

Have you tried shaking the bucket/bag before scooping out the salt mix? Sometimes as boxes/buckets of salt sit some of the chemicals tend to sit at the bottom and shaking it before mixing saltwater may help.

 

[anthonygf]

Have you tried shaking the bucket/bag before scooping out the salt mix? Sometimes as boxes/buckets of salt sit some of the chemicals tend to sit at the bottom and shaking it before mixing saltwater may help.

I can't with the Fritz, they have one bag and it is about 60 pounds, the RC box has 4 bags and was easy to mix.

 

[Aaron Shapiro]

Have you tried shaking the bucket/bag before scooping out the salt mix? Sometimes as boxes/buckets of salt sit some of the chemicals tend to sit at the bottom and shaking it before mixing saltwater may help.

Yeah I did that.

 

[Randy Holmes-Farley]

New salt water with higher alk is especially prone to precipitation of calcium carbonate. Much more so than once it is in the aquarium because there are no organics or phosphate to reduce the ongoing rate of precipitation by binding to fresh calcium carbonate surfaces.

What is that Precipitate in My Reef Aquarium? by Randy Holmes-Farley - Reefkeeping.com

Figure 1. The residue on the bottom of the plastic trash can that I use to mix Instant Ocean. I rarely clean it out. The solid is most likely calcium carbonate.

Solid Residues Remaining After Preparing Artificial Seawater
Most salt mixes leave behind a solid residue when dissolved, although the extent to which this occurs varies from brand to brand. I use Instant Ocean and rarely clean out the 44-gallon trashcan that I mix it in, so a significant residue builds up over time (Figure 1). In preparation for this article I removed some of this solid material, and found that it could be almost completely dissolved in hydrochloric acid with lots of bubbling. This demonstrates that these solids were probably calcium carbonate (CaCO3), perhaps also containing magnesium. Pure magnesium carbonate is undersaturated in seawater (which is detailed in later sections of this article) 1 and should dissolve in marine systems, so it isn't likely to be the precipitated material, although there may be significant magnesium in the calcium carbonate.

Based on the fact that the material exists as sheets that clearly did not arrive in the mix (as opposed to a fine powder which might have), I conclude that at least a significant fraction of this residue formed in the barrel. I cannot, however, rule out the possibility that some solid calcium or magnesium carbonate may have existed in the salt mix and was cemented together by additional precipitation of calcium carbonate during dissolution or storage.

When salt mixes are dissolved, there exist local regions where the salt concentration is very high. In those local regions, the calcium and alkalinity must also be very high. In fact, as seawater is concentrated by evaporation, there is a well-established series of minerals that precipitate as the salinity increases. In this series, calcium and magnesium carbonate are the first to precipitate, appearing at a specific gravity of about 1.140, which is about a 50% solution of salt in water.1 Such conditions may well exist on the bottom of a saltwater reservoir as the salt is dissolving.

With some mixes (but not the Instant Ocean that I use), the initial pH on dissolution may be very high (pH 8.5-9 +). As shown in detail later in this article, pH can play a dominant role in determining the rate of calcium carbonate precipitation, and such a high pH would make it more likely to precipitate.

It has been suggested by some aquarists that some salt mixes may contain anti-caking agents, such as clays. I do not know if this is true, but if it is, they may form part of the residue that is left behind after dissolution.

In order to minimize the formation of insoluble carbonate salts when mixing, the following suggestions may be helpful:

1. Add the salt to a full batch of water, rather than adding water slowly to a large batch of salt. The latter allows a greater time at much higher than natural seawater salinity, which may tend to precipitate calcium and magnesium salts.

2. Stir the mixture vigorously as it is being dissolved.

3. If using a mix with a high initial pH, aerate the mixture as well as stirring it. The aeration will reduce the pH.

 

[Aaron Shapiro]

New salt water with higher alk is especially prone to precipitation of calcium carbonate. Much more so than once it is in the aquarium because there are no organics or phosphate to reduce the ongoing rate of precipitation by binding to fresh calcium carbonate surfaces.

What is that Precipitate in My Reef Aquarium? by Randy Holmes-Farley - Reefkeeping.com

Figure 1. The residue on the bottom of the plastic trash can that I use to mix Instant Ocean. I rarely clean it out. The solid is most likely calcium carbonate.

Solid Residues Remaining After Preparing Artificial Seawater
Most salt mixes leave behind a solid residue when dissolved, although the extent to which this occurs varies from brand to brand. I use Instant Ocean and rarely clean out the 44-gallon trashcan that I mix it in, so a significant residue builds up over time (Figure 1). In preparation for this article I removed some of this solid material, and found that it could be almost completely dissolved in hydrochloric acid with lots of bubbling. This demonstrates that these solids were probably calcium carbonate (CaCO3), perhaps also containing magnesium. Pure magnesium carbonate is undersaturated in seawater (which is detailed in later sections of this article) 1 and should dissolve in marine systems, so it isn't likely to be the precipitated material, although there may be significant magnesium in the calcium carbonate.

Based on the fact that the material exists as sheets that clearly did not arrive in the mix (as opposed to a fine powder which might have), I conclude that at least a significant fraction of this residue formed in the barrel. I cannot, however, rule out the possibility that some solid calcium or magnesium carbonate may have existed in the salt mix and was cemented together by additional precipitation of calcium carbonate during dissolution or storage.

When salt mixes are dissolved, there exist local regions where the salt concentration is very high. In those local regions, the calcium and alkalinity must also be very high. In fact, as seawater is concentrated by evaporation, there is a well-established series of minerals that precipitate as the salinity increases. In this series, calcium and magnesium carbonate are the first to precipitate, appearing at a specific gravity of about 1.140, which is about a 50% solution of salt in water.1 Such conditions may well exist on the bottom of a saltwater reservoir as the salt is dissolving.

With some mixes (but not the Instant Ocean that I use), the initial pH on dissolution may be very high (pH 8.5-9 +). As shown in detail later in this article, pH can play a dominant role in determining the rate of calcium carbonate precipitation, and such a high pH would make it more likely to precipitate.

It has been suggested by some aquarists that some salt mixes may contain anti-caking agents, such as clays. I do not know if this is true, but if it is, they may form part of the residue that is left behind after dissolution.

In order to minimize the formation of insoluble carbonate salts when mixing, the following suggestions may be helpful:

1. Add the salt to a full batch of water, rather than adding water slowly to a large batch of salt. The latter allows a greater time at much higher than natural seawater salinity, which may tend to precipitate calcium and magnesium salts.

2. Stir the mixture vigorously as it is being dissolved.

3. If using a mix with a high initial pH, aerate the mixture as well as stirring it. The aeration will reduce the pH.

hey Randy,

this is helpful but I’m confused on a few things... I use a power head to mix the water and generally let it mix an hour or two prior to adding to the aquarium. I haven’t noticed a big precipitate at the bottom of my buckets but I’m only mixing ~5g at a time.

would more or less mixing time effect any precipitation??

 

[Randy Holmes-Farley]

hey Randy,

this is helpful but I’m confused on a few things... I use a power head to mix the water and generally let it mix an hour or two prior to adding to the aquarium. I haven’t noticed a big precipitate at the bottom of my buckets but I’m only mixing ~5g at a time.

would more or less mixing time effect any precipitation??

Yes, the longer you mix (and especially heating it), the more potential for precipitation.

If you see no precipitate, maybe the issue lies elsewhere, such as faulty testing, or a low alk batch of salt.

 

[KevinC]

thats weird. my fritz salt alk is about 7.5

 

[anthonygf]

hey Randy,

this is helpful but I’m confused on a few things... I use a power head to mix the water and generally let it mix an hour or two prior to adding to the aquarium. I haven’t noticed a big precipitate at the bottom of my buckets but I’m only mixing ~5g at a time.

would more or less mixing time effect any precipitation??

Hi Aaron. I mix mine the same way, 5 gallon bucket, 50 watt heater and I use a small pump with 1/2" clear hose for mixing and then pump the water into the sump. What test kit are you using to test your water? And mix for about an hour or two.

 

[Aaron Shapiro]

Hi Aaron. I mix mine the same way, 5 gallon bucket, 50 watt heater and I use a small pump with 1/2" clear hose for mixing and then pump the water into the sump. What test kit are you using to test your water? And mix for about an hour or two.

salifert and Redsea alk tests.

 

[anthonygf]

salifert and Redsea alk tests.

I like Hanna, tried them all and it is very easy to use, also I think it is most accurate.

 

[Aaron Shapiro]

I like Hanna, tried them all and it is very easy to use, also I think it is most accurate.

That hasnt been my experience, at least not for alk. I recently sold my Hanna alk tester.

 

[Randy Holmes-Farley]

I like Hanna, tried them all and it is very easy to use, also I think it is most accurate.

How do you know which test is more accurate?

 

[anthonygf]

How do you know which test is more accurate?

I have gotten more consistent readings, it may be off by a little +or- a few points but as long as alk stays consistent isn't that what is most important?

 

[anthonygf]

That hasnt been my experience, at least not for alk. I recently sold my Hanna alk tester.

Maybe a bad meter? I have been using mine for over 3 years and still is reliable. I also still have a Salifert alk test kit which I use occasionally just to verify it is within range.

 

[Randy Holmes-Farley]

I have gotten more consistent readings, it may be off by a little +or- a few points but as long as alk stays consistent isn't that what is most important?

That may be true, but you claimed more accurate, and few folks actually know if their alkalinity devices are accurate or not. I just wanted to clarify as the meaning of consistent and accurate are very different.

 

[anthonygf]

That may be true, but you claimed more accurate, and few folks actually know if their alkalinity devices are accurate or not. I just wanted to clarify as the meaning of consistent and accurate are very different.

So true, sorry for that. I meant consistent.