Watermaker layup: old Sodium Metabisulphite

[Tim Good]

Im laying up my watermaker for 6 months and the tub of Sodium Metabisulphite powder which I'm meant to dissolve in fresh water has gone all hard. I can scrape it in chunks and then grind it to powder again but do you think that'll be ok or does this stuff have a shelf life?

It's an old Aquafresh AF600. 70grams of Sodium Metabisulphite per 20litres is the dosage.

If I'm unsure can I used extra Sodium Metabisulphite without any harm?

 

[VicS]

Re: Watermaker layup: old Sodium Metabisulfite

In a tightly capped glass or plastic container it should keep..... but it should not go hard. I'd say it has had it, especially if you can grind it back to a powder without being overcome by sulfur dioxide

 

[NOHOH]

Get a 5 gallon plastic drum with a good tight cap....preferably translucent so you can see what is inside...put the whole 70 grams of metabisuiphite in (you don`t need to grind it up...just break it into small enough lumps to go into the drum) and add about a gallon of water........Give it a really good shake up....then leave it for an hour or so....then repeat the shaking and waiting until its all dissolved...then dilute to the correct concentration.....
I`ve been using this method for about 10 years with no detrimental effects to me or the watermaker. I cant see how it can `go off` in any serious way....its an inorganic compound.

 

[VicS]

Re: Watermaker layup: old Sodium Metabisulfite

Get a 5 gallon plastic drum with a good tight cap....preferably translucent so you can see what is inside...put the whole 70 grams of metabisuiphite in (you don`t need to grind it up...just break it into small enough lumps to go into the drum) and add about a gallon of water........Give it a really good shake up....then leave it for an hour or so....then repeat the shaking and waiting until its all dissolved...then dilute to the correct concentration.....
I`ve been using this method for about 10 years with no detrimental effects to me or the watermaker. I cant see how it can `go off` in any serious way....its an inorganic compound.

Loss of sulfur dioxide ? Fairly serious if you are using it as a source of SO₂

 

[NOHOH]

Maybe....but only if you keep it in an open container for years.......which common sense dictates against. Please follow my suggestion and you wont go wrong.

 

[Tim Good]

Maybe....but only if you keep it in an open container for years.......which common sense dictates against. Please follow my suggestion and you wont go wrong.

Yeah I have a specific 25L tub which I use only for the water maker. Dissolve about 70-90g in 25 litres and then circulate. It does dissolve eventually but I was more curious if it wouldn't go off.

I have a few other questions whilst I'm here:

- can I over dose on this stuff? If I leave the watermaker for over a year then should I go the extra mile
I use more powder?
- do you leave your filters in their cartridges whilst decommissioned or remove and dry?

 

[VicS]

Maybe....but only if you keep it in an open container for years.......which common sense dictates against. Please follow my suggestion and you wont go wrong.

Yeah I have a specific 25L tub which I use only for the water maker. Dissolve about 70-90g in 25 litres and then circulate. It does dissolve eventually but I was more curious if it wouldn't go off.

I have a few other questions whilst I'm here:

- can I over dose on this stuff? If I leave the watermaker for over a year then should I go the extra mile
I use more powder?
- do you leave your filters in their cartridges whilst decommissioned or remove and dry?

If has gone completely hard then it clearly has not been stored very well and you have no way of knowing the extent to which it has deteriorated.

I have two jars of laboratory grade sodium metabisulfite which have been on the shelf for about 40 years . They have not gone hard. They are both still free running powder.

 

[Tim Good]

They have not gone hard. They are both still free running powder.

Stored in a garage or on a boat in the water?

 

[Mistroma]

Stored in a garage or on a boat in the water?

I have a bottle on-board and it must be around 30-40 years old. It is still free flowing apart from bottom inch in the bottle. I don't use it much and it has lasted forever. I think that I did finish another bottle about 10 years ago.

I have just poured it out to check the material at the bottom of the jar. It wasn't too difficult to break up and is certainly still effective. No big problem storing it on my previous and current boats over a 30 year period.

I'd agree with VicS that it's important how you store it. It won't matter much where it is stored if used infrequently and left well sealed.

I saw a comment above indicating that inorganic compounds could not degrade significantly. That's obviously not always correct. It's true that you can leave plenty of stable inorganic materials lying around forever because they are inherently stable. However, there are plenty of highly reactive inorganic materials which will readily react with air, moisture etc.

Look up Dioxygen Difluoride if you want to see an exotic extreme. There's a whole range of inorganics from stable over millennia to instantly decompose. I've seen a variety of inorganic compounds go bang or set fire to wood after drying.

Inorganic does not mean inert or not reactive.

 

[ghostlymoron]

Considering the relative values of a bottle of sodium metabisulphite and a water maker, I would buy some fresh stuff.

 

[Tim Good]

Considering the relative values of a bottle of sodium metabisulphite and a water maker, I would buy some fresh stuff.

Yes that's the plan but I posted the thread as I'm laying the boat up now and don't have access to fresh stuff on the island on El Hierro in the Canaries.