Salt mix that doesn't dissolve completely

[OB1]

What good are trace minerals that don't completely dissolve? I've tried several salt mixes and there is always some residue left no matter how long I let it mix. It doesn't seem to cause any problems but is just annoying. Which salt mix do you use that completely dissolves??

[tinyreef]

how are you mixing the salts? salt in container first, and then water? are you using cold water? is the water distilled-RO-RO/DI or tapwater or some other type (e.g. spring)?

 

all these salts contain CaCl and some type of buffers (e.g. carbonates). if mixed in certain fashions, the salt can supersaturate and cause the CaCl and carbonates to prematurely combine (precipitate) to become tiny calcium carbonate (rock/sand) nuggets and salt (NaCl), which those leftover could be.

 

try lowering your concentrations and then build upwards. it's ok to start with 1.010, and then add salt to creep up to the target sg/salinity level. this will lessen the chance of saturating the mix and precipitating the CaCO3.

[andre]

your water may be too cold? thats been an issue with my salt before but usually a heater takes care of it

[Mr. Fosi]

try lowering your concentrations and then build upwards.

 

Or, since you have already precipitated mix laying around, add half a liter of store-bought plain carbonated water to it and drop in a powerhead. Precipitate will re-dissolve and you can drive the CO2 back out of solution by aerating it overnight.

[Normandy]

I find adding a quart or so of bleach helps.

[Mr. Fosi]

Very helpful response Normandy, thanks for your input.

[xbwolfx]

since tiny mentioned it, i've been wondering if i should heat the water to 78-80f before adding salt. now that it is cold outside, i've noticed that i get a film on the surface of my salt water. i've been adding the salt to the cold water and then letting it heat up during mixing. my problem could also be that the trash can i use to mix salt in needs a good vinegar bath, though.

[Mr. Fosi]

Heating the water can't hurt you but I am curious about what this film looks like.

[xbwolfx]

Heating the water can't hurt you but I am curious about what this film looks like.

to be honest, it isn't very bad and would likely go away if i mixed the water longer. also, better surface agitation would help too. it is oceanic salt. i have had this problem in the past and i think i just need to give my trash can a vinegar bath. i usually just rinse it with tap water every week and probably don't do as good of a job as i should.

[EasyEd77]

I have never had a problem with Tropic Marin Pro salt leaving a residue. On the other hand when I used Red Sea Coral Pro I did get residue.

[Normandy]

I have never had a problem with Tropic Marin Pro salt leaving a residue. On the other hand when I used Red Sea Coral Pro I did get residue.

 

I've had this same experience. I've also noticed that salt from a new box/bucket is less likely to leave remaining solids than from a batch that has been open for some time.

[Mr. Fosi]

That's because artificial sea salt is hygroscopic. As it absorbs moisture in the air you get localized supersaturation and very high pHs which leads to precipitation of CaCO₃ and other compounds.

 

Evidence from tests I have done on my own salt mixes indicates that if you get precipitation during your mixing, you can easily redissolve the precipitate my lowering the pH of the mix. Adding half a liter of soda water will drag the pH of your SW down below 5, which is much further than you need to get the precipitate to redissolve but it will do it fast and without any lasting effects.

 

Obviously, you don't want to add pH 5 SW to your tank but since the pH depression was caused by the CO₂ in the soda water, you can drive the excess out solution by aerating it. It doesn't "want" to be at a pH of 5 because that is radically out of equilibrium with the overlying air. Given time, the pH will come back up on it's own but without vigorous mixing, you will have to wait a long time.

[Normandy]

That's because artificial sea salt is hygroscopic. As it absorbs moisture in the air you get localized supersaturation and very high pHs which leads to precipitation of CaCO₃ and other compounds.

 

Evidence from tests I have done on my own salt mixes indicates that if you get precipitation during your mixing, you can easily redissolve the precipitate my lowering the pH of the mix. Adding half a liter of soda water will drag the pH of your SW down below 5, which is much further than you need to get the precipitate to redissolve but it will do it fast and without any lasting effects.

 

Obviously, you don't want to add pH 5 SW to your tank but since the pH depression was caused by the CO₂ in the soda water, you can drive the excess out solution by aerating it. It doesn't "want" to be at a pH of 5 because that is radically out of equilibrium with the overlying air. Given time, the pH will come back up on it's own but without vigorous mixing, you will have to wait a long time.

 

Thank you for the insight.

[OB1]

your water may be too cold? thats been an issue with my salt before but usually a heater takes care of it

Next time I'll heat the water before I add the salt. I've always just put the salt mix right in the cold water then let it heat as it mixed.