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Old 07-08-2009, 06:56 PM   #1
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Residue in water mixing bin

Hey everybody,

I recently started noticing a sandy colored residue in the bin that I use for mixing my saltwater. I use reef crystals. I have never seen this residue before. This last water change I noticed it when the salt was mixed in and sat over night with a power head for circulation. Next time I will check and see if the residue is there before I add the salt.
Have you guys noticed this as well?
My lfs indicated that it was ok and they get it as well. Something to do with minerals?
Anyhow I thought it might be my resins in my RO but they are only 3 months old.
Just wondering........
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Old 07-09-2009, 01:59 AM   #2
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I use Reef Crystals also and have the same stuff in my storage tub. I've always assumed it's just calcium carbonate - whatever it is though I don't think it's an issue. I've never seen any problems with my new water and it's always done it for me, using DI water with 0 TDS.
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Old 07-09-2009, 09:15 AM   #3
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I do mix w/ RO water. You are right with CACO3 precipitation.
My next question is if there is this precipitation happening, does that mean then that the Ca, Mg, and Alk levels be less in the newly mixed water?
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Old 07-09-2009, 04:07 PM   #4
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I've wondered that myself, but have never noticed any decrease in ca/alk/mag levels in the stored water.
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Old 07-09-2009, 04:30 PM   #5
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Quote:
Originally Posted by jsdancer View Post
My next question is if there is this precipitation happening, does that mean then that the Ca, Mg, and Alk levels be less in the newly mixed water?
Not necessarily esp if there was high levels anyway.
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Old 07-12-2009, 11:05 AM   #6
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What is that Precipitate in My Reef Aquarium?
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.
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Old 07-14-2009, 04:16 AM   #7
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Thanks Larry, that's great information.
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Old 07-18-2009, 01:45 AM   #8
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Thank you for the info. I will try your approach on my next water change.
Initally I never had a residue from using IO even when adding it to a small batch of water. As the RO/DI water continued filling the trash can I would mix.
Once I started to use RC then things changed and I would also leave the newly mixed batch for at least 24 hrs before doing my water change thus allowing more time for the precipitation to occur.
I will try it your way.
Thanks Capt
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