Does artificial salt deteriorate?

[New Reefer]

I usually use "fresh" seawater for my partial water changes, but do occasionally use artificial mix when the weather is bad, or when I'm just too lazy to drive ~40km to get the water. I thus do not use much artificial salt - in fact, I have just used the last of a 20kg supply bought more than 18 months ago...

I would appreciate it if you could answer the following:

1. Does artificial salt mix deteriorate with time if stored in it's original (sealed) container - if so, how long can it be stored?

2. Does artificial salt deteriorate after the container has been opened, and the salt exposed to air (moisture...) - if so, what would the effects be, and for how long can it be stored? Also, can one re-dry the salt to improve it's "storeability"

3. Are there any DIY tests, etc. to determine if the salt mix is still OK?

4. Any comments / suggestions on the storage of salt?

Thanks,
Hennie

[Drew_P]

i had a 25 gallon filled with fresh fake saltwater with just a powerhead it was in the tank for about 6 months the i decided after some rock and scrap sand with a filter and skimmer it was established enough so i did a 25 gallon water change in my 120

[New Reefer]

Scleropages:

i had a 25 gallon filled with fresh fake saltwater with just a powerhead

Actually, I'm inquiring about the dry salt, before you add water...

[chris_h]

Only when it gets exposed to moisture. When it is exposed to moisture, the carbonate and the calcium join and will not disolve.

[Randy Holmes-Farley]

The concern that Chris has about precipitation of calcium carbonate would be my biggest concern as well. I believe, however, that it can happen even is closed bags, though it may be faster if opened in a humid environment and exposed to additional CO2.

FWIW, I had some unpoened bags of Coralife salt sitting around for a long time (years). Eventually, they got very, very hard and stiff. I presume that CaCO3 slowly precipitated.

That said, even the precipitation of some of the CaCO3 isn't a show stopper if you are on a very tight budget. If you just let it settle to the bottom when dissolving and don't add it to the tank, all you will need to do is add more calcium and alkalinity for a time (this presumes that you are doing so already). I would not use this to start a new tank or do a huge water change, however.

There is a concern that other things may be precipitating too, but many of these should redissolve in tank water.

[New Reefer]

Thanks, guys...

I've just tested the alkalinity of the mix I made yesterday (using the last of the ~18 month old salt.)

dKH = 5

This ties in with Chris and Randy's theory - I guess that I will have to buy smaller volumes of salt in the future.

Randy, why do you recommend that the precipitated CACO3 be discarded, and not added to the tank? Is this not the same as aragonite? Would it not just become part of the live sand eventually?

Hennie

[MickAv8r]

Originally posted by New Reefer
I usually use "fresh" seawater for my partial water changes, but do occasionally use artificial mix when the weather is bad, or when I'm just too lazy to drive ~40km to get the water.

40km for water in South Africa? Is it laziness or too dangerous heh, I have a friend that heads down there to train police departments every year or so, says the crime is getting insane down there. Stay safe!

[New Reefer]

MickAv8r:

Is it laziness or too dangerous heh,

No, just laziness

I'm fortunate to be living in a very quiet, safe part of South Africa - on the Cape south coast. It's just that the ocean is about 30km away from where I stay, and I prefer to collect my water about 10 km further - further away from a river mouth, in a very quiet, unpolluted part of the beach. I usually collect the water from thr rocks, during high tide. The "difficult" part is hauling 25l containers about 400m uphill through loose beach sand to get to the car - I usually collect about 150l of water, and that's quite an effort

Hennie

[Randy Holmes-Farley]

Hennie:

<< why do you recommend that the precipitated CACO3 be discarded, and not added to the tank? Is this not the same as aragonite? Would it not just become part of the live sand eventually?>>

Yes and no. Adding fresh aragonite isn't good for aquaria. It immediately acts as a nucleating site for precipitation of calcium and alkalinity as CaCO3. That's why, for example, adding a bunch of CaCO3 sand will have an immedate effect on the pH, calcium, and alkalinity in a reef tank (they all drop).

In a few hours this process stops because the surface of the CaCO3 becomes clogged with magnesium, phosphate, organics, and possibly other things. It then no longer nucleates additional CaCO3 precipitation, and becomes the sand beds that we all know.

[New Reefer]

Thanks, Randy - that makes it quite clear.

Another (stupid?) question on the same topic, if I may:

When mixing the water, would adding the salt first, and then the water, cause any problems (I usually do it the other way round, so just curious...)

What I'm thinking of is perhaps with all the salt in the bucket, when one starts to add water, the solution would be very concentrated (saturated?) - would this not cause the calcium to start precipitating while one is still busy adding the water?

Thanks,
Hennie

[Randy Holmes-Farley]

Hennie:


<< would this not cause the calcium to start precipitating while one is still busy adding the water? >>

That's not a stupid question at all (stupid questions rarely require a long response!), and even if some questions do seem that way to advanced aquarists, they are almost always useful to some hobbyists. So keep em coming!

Again, the answer is yes and no. Calcium carbonate is supersaturated in seawater, and may be much more so if you add a small amount of water to salt mix solids (or for that short period where you have a little water and are still pouring in more).

One reason that CaCO3 can be supersaturated in seawater is that it is really slow to nucleate. That is, in the absence of any seed crystals, calcium carbonate is slow to precipitate. I don't know all of the reasons for this, but it may go back to the reason that solid sand beds no longer act as such sources: even if a microscopic CaCO3 seed forms, it my become clogged with magnesium, organics, etc, before it can really get started to do substantial precipitation of CaCO3.

In any case, the same effect should help protect it when dissolving salt: the transient large supersaturation may simply not have time to result in much precipitation before it is diluted back to norrmal levels.

FWIW, I have made salt mix both ways, but have never really tested them to see if they were equivalent. In many setups, it is convenient to have the pouring of water into the bucket supply the mixing necessary to cause most of the dissolution.

However, going back to your original question. IMO, it is clearly "better" to add the salt to the water than the other way around. However, whether "better" ends up being significant or not in a real application, I cannot say.