last night i attempted to raise the alk of my tank (soda ash) discontinued batch 3 years of age. I attempted to raise 6.9 to 7.5 , just a hour ago i checked the alk and its 7.1. I got some precipitation small snow storm when dripping with a 5ml sryinge into a gyre at full power . To prepare i followed brs instructions , does sodium bicarbonate precipitate less ? or at all? compared to soda ash
Brs soda ash
- Thread starter LOVEROCK
- Start date
- Tagged users None
Randy Holmes-Farley
Reef Chemist
Staff member
Super Moderator
Excellence Award
Expert Contributor
Article Contributor
R2R Research
My Tank Thread
It is normal to see precipitation of magnesium hydroxide when dosing high pH additives;
Precipitates When Carbonate Solutions are Added
Many aquarists are familiar with the cloudiness that forms when high pH two-part calcium and alkalinity additive systems are added to marine aquaria. Figure 3 shows the initial cloud that forms, for example, when the alkalinity part of B-ionic is added to a relatively low flow reef aquarium. The initial cloud sinks and spreads out, eventually dissolving. A similar phenomenon is not observed when adding calcium or magnesium salts, but is observed when adding sodium carbonate solutions.
This cloudiness is, at least in part, magnesium hydroxide and is formed when hydroxide ions are added and the local pH rises. Unlike the addition of limewater, which is unlikely to form magnesium carbonate, this may, although I think it unlikely. The reason it might form here is that the addition of the carbonate ions may push the magnesium carbonate solubility product above saturation. The precipitation of magnesium carbonate can be kinetically slow, just as the precipitation of calcium carbonate can be slow, and since this cloudiness forms instantly, magnesium hydroxide is a much more likely candidate. However, if the additive is not rapidly mixed in, or worse yet, if solid globs of the initial precipitate settle out and are very slow to dissolve, then conditions may be ripe for magnesium carbonate (and calcium carbonate) to form.
In any case, any magnesium carbonate that does form will probably dissolve later as the pH returns to normal reef aquarium levels, so whether the initial cloudiness contains any magnesium carbonate or not is not a critical issue. It does not contain calcium carbonate if mixed in reasonably quickly (a couple of minutes or less), as CaCO3 would not dissolve when mixed with seawater (and this material is observed to dissolve).
Precipitates When Carbonate Solutions are Added
Many aquarists are familiar with the cloudiness that forms when high pH two-part calcium and alkalinity additive systems are added to marine aquaria. Figure 3 shows the initial cloud that forms, for example, when the alkalinity part of B-ionic is added to a relatively low flow reef aquarium. The initial cloud sinks and spreads out, eventually dissolving. A similar phenomenon is not observed when adding calcium or magnesium salts, but is observed when adding sodium carbonate solutions.
This cloudiness is, at least in part, magnesium hydroxide and is formed when hydroxide ions are added and the local pH rises. Unlike the addition of limewater, which is unlikely to form magnesium carbonate, this may, although I think it unlikely. The reason it might form here is that the addition of the carbonate ions may push the magnesium carbonate solubility product above saturation. The precipitation of magnesium carbonate can be kinetically slow, just as the precipitation of calcium carbonate can be slow, and since this cloudiness forms instantly, magnesium hydroxide is a much more likely candidate. However, if the additive is not rapidly mixed in, or worse yet, if solid globs of the initial precipitate settle out and are very slow to dissolve, then conditions may be ripe for magnesium carbonate (and calcium carbonate) to form.
In any case, any magnesium carbonate that does form will probably dissolve later as the pH returns to normal reef aquarium levels, so whether the initial cloudiness contains any magnesium carbonate or not is not a critical issue. It does not contain calcium carbonate if mixed in reasonably quickly (a couple of minutes or less), as CaCO3 would not dissolve when mixed with seawater (and this material is observed to dissolve).
blasterman
Valuable Member
- Joined
- Feb 14, 2019
- Messages
- 1,730
- Reaction score
- 2,025
Randy - when I can I use kalk for dosing because it kills two birds with one stone and you get elevated pH as a bonus. When consumption gets too high then kalk obviously cant keep up other than for top offs.
I add kalk powder directly to the tank via shaking up the powder in a juice jug and pouring it in the tank. A teaspoon per 10gal at a time is my max. This turns the water pretty milky due to carbonate dissolution and sometimes leaves a little white precipitate. This dissolves quickly though and corals never react.
Reefers treat the carbonate residue just like with mag hydroxide as some of kind of toxic byproduct and it's not. It's the most easily soluble form of calcium there is for coral. The good stuff is at the bottom of the jug
I add kalk powder directly to the tank via shaking up the powder in a juice jug and pouring it in the tank. A teaspoon per 10gal at a time is my max. This turns the water pretty milky due to carbonate dissolution and sometimes leaves a little white precipitate. This dissolves quickly though and corals never react.
Reefers treat the carbonate residue just like with mag hydroxide as some of kind of toxic byproduct and it's not. It's the most easily soluble form of calcium there is for coral. The good stuff is at the bottom of the jug
