White powdery crud in salt water mix

[sen5241b]

After a couple days I noticed some white powdery, flaky crud in the salt water mix I prepared. I had a pump and heater in there to keep it going but it settled on the bottom. I dumped it out and started over ensuring the container was clean. (No soap was used). After a couple days the white crud settles in again on the bottom --what is that stuff? Unmixed salt? Anyone else seen this? I always use Oceanic but I've never seen this before.

[zygote2k]

I have the same result from using I/O. I just mix it back into the next batch and never gave it much thought. Maybe it's excess mineral salts of some sort?

[Hilary]

I get the same thing. Right or wrong I just leave it and haven't had any issues. Every so often I dump out that last 2-3 gallons and scrub out the bottom.

[steveoutlaw]

I get it as well. I just wipe my container out after every batch I make.

[dbartco]

After about 8 months or so I have to take a hammer and beat the heck out of my trashcans to get the encrusted deposits out. Fill with tap water and muratic acid, to clean, ans restart.

[www.fishnreef.com]

It seems to be better to add salt to more water vs. less as adding salt to a little water supersaturates the liquid which may then percipitate out.

[Origami]

Most of the time, it's just calcium carbonate that precipitates out in areas of especially high concentration as the salt mix dissolves. RHF had an article in 2005 that you may be interested in (http://reefkeeping.com/issues/2005-07/rhf/index.php). He writes,

 

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.

 

 

(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. )

 

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.

[blaze98]

I normally mix my salt in an unused aqaurium, but I have a powerhead and heater already going before I add any salt and I never get anything left over.

[blaze98]

I use IO salt by the way

[onux20]

I mix Reef crystals in a 13gal trash can with a mag 3 and heater. I get that brown stuff all the time. Like Hilary, i just give it a good scrub once in a while.

 

Great article...it answered several of my questions.

 

Ron

[sen5241b]

I mix Reef crystals in a 13gal trash can with a mag 3 and heater. I get that brown stuff all the time. Like Hilary, i just give it a good scrub once in a while.

 

Great article...it answered several of my questions.

 

Ron

 

 

I got 'white' crud. I used a new jug of Oceanic and the water was a clear in 10 minutes, I think there is a settling of contents with some batches.