Epsom salt

[Gideyon]

I have a bag of epsom salt that says MGSO4 7H2O

I can't find any info on this if it is pure epsom salt or something not safe for fish.  This 7H2O part throws me off.  The active ingredients say magnesium sulfate only.  

 

Anyone know?  

[Guppysnail]

Yes 7h2o simply means its combined with 7 molecules of water. 
 

it reads as magnesium sulfate heptahydrate meaning its processing is done with water

Edited July 19, 2021 by Guppysnail
Add better explanation

[Gideyon]

Thanks. I finally read somewhere that that is what epsom salt is.  

 

Didn't want to hurt my already hurt fish with something that wasn't epsom salt. 

[Guppysnail]

On 7/19/2021 at 3:22 PM, Gideyon said:

Thanks. I finally read somewhere that that is what epsom salt is.  

 

Didn't want to hurt my already hurt fish with something that wasn't epsom salt. 

I only know that because at one point i had to look it up for myself🤣

[Hobbit]

Ahh teacher mode activated! 😅

On 7/19/2021 at 3:20 PM, Guppysnail said:

meaning its processing is done with water

Close! You are right about the 7H2O just being extra water in there, but (if I remember correctly) this doesn’t refer to a specific kind of processing.

Most salts will absorb some amount of water out of the air. So in this case it’s saying they let it absorb 7 molecules of H2O per magnesium sulfate molecule. I have no idea if that’s the amount it would normally absorb or if they dehydrated it a bit before packing.

Some salts absorb so much water out of the air that they turn into a goopy glob. Others absorb very little. It just depends on what they’re made of.

[CT_]

Make sure any "recipe" you use assumes you have the heptahydrate.  That changes the molecular weight.  but I think 7H2O is the most common. 

 

In case anyone ends up with anhydrous in the future and reads this, be careful with that too.  It can get REALLY hot when you add water.

[Hobbit]

I don’t think the exact hydrate count will matter much for most aquarium-related recipes—and hopefully if an aquarist gets their hands on anhydrous Epsom salts, it’s because they work in a lab and already know what they’re doing! 😅

Just don’t want anyone to panic. 👍

[CT_]

On 7/30/2021 at 11:31 PM, Hobbit said:

I don’t think the exact hydrate count will matter much for most aquarium-related recipes—

Good points.  I did some looking and it sounds like if it's called epsom salt it's heptahydrate. 

 though it looks like if you do get them mixed up you could be off by a factor of 4 if you measure by volume.

On 7/30/2021 at 11:31 PM, Hobbit said:

and hopefully if an aquarist gets their hands on anhydrous Epsom salts, it’s because they work in a lab and already know what they’re doing!

Heh you'd think so but it was quite a surprise when I put anhydrous salts into media for the first time as a grad student.

[Hobbit]

On 7/31/2021 at 9:32 PM, CT_ said:

Good points.  I did some looking and it sounds like if it's called epsom salt it's heptahydrate. 

 though it looks like if you do get them mixed up you could be off by a factor of 4 if you measure by volume.

Wow, that’s more than I expected! I did find one website selling hexahydrate epsom salts. Hopefully the margins aren’t too close on any of these recipes, but it’s certainly good to be aware of what you have.