Calcium Bleedin' Sulphate

[Vale!]

I post this just in case it may help a future fellow ignoramus ...

I'm making a 'new' water recipe (well, new to Vale! Towers that is) which calls for an amount of calcium bleedin' sulphate. So merrily, a few hours ago, I filled a 2L jug with RO/DI water and gave it a few minutes in the microwave so that it would dissolve more easily.

Yes?

No!

After a deal of time had elapsed during which I attacked it successively with : a rampant spoon ; then a whisk ; and then an electric blender, it still looked like a jugful of Tesco semi-skimmed.

In my anguish I turned at last to Google. Did you know that the closer to freezing a mixture of calcium bleedin' sulphate is, the better it dissolves? Talk about counter-intuitive!

So it'll be sitting in the fridge overnight. I shall report back. Grrr!

[plankton]

I would never have guessed that......

[fr499y]

It certainly is a strange one!

[Vale!]

Morning report ...

Well it definitely looks less milky but it's nowhere near a complete solution! And there's still a layer of undissolved stuff on the bottom. There's 3.84 grams of CalSulph in the jug. I'm conscious that it could have already reached saturation, so I'll do some diluting if I need to later on.

This pic was taken before I gave it a damn good thrashing, Basil Fawlty style, with a whisk:



Temperature was 6.4C and conductivity 588uS.

I've now put it in the freezer for an hour or two where it can think about what it's done.

[fr499y]

Have you tried running an air stone for a few hours? It might alter it slightly as it will introduce co2 from the air, but should help it dissolve (that combined with the colder temperature).

[Vale!]

Seems like a plan, M!

A bit of further reading turned up someone (in a lab) who routinely made solutions of calcium sulphate in 25L batches using your suggested method. He reported that it took 'several days' of vigorous 24hr bubbling. He blamed this on the fact that dissolved CO2 only "equilibriated" with atmosphere.

Because my tanks (mostly) run at relatively low pH they have more dissolved CO2 in them than do 'normal' tanks. So maybe I can artificially introduce it by mixing in tankwater? This is what I'm trying now.

Whilst waiting for the freezer to do its work again here's an interim report. This is fast becoming a matter of honour!


I whisked the jug and put 200mls of its contents into a glass (6.8C ; 602uS ; pH7.28) then added 200mls of tankwater (27C ; 78uS ; pH 5.61)



Result after 10mns : still milk, with layer of undissolved salt in the bottom (19C ; 472uS ; pH7.07). I've put the glass in the freezer for half-an-hour.

The only reservation I have about this acidification method is that it works (if it will do at all in my glass) by way of producing calcium carbonate and ammonium sulphate, both of which are eminently more soluble. But the recipe calls for calcium sulphate, not calcium carbonate! I've been back to the source for the recipe (Cornell and Penn State universities) intending to ask them how they do it, but I can't see a contact address for the specific programme (sorry, program) which generated this 'optimum' water. *sigh*

[Vale!]

With a sudden burst of inspiration I looked for ready-made calcium sulphate solution (fancying that maybe the construction industry might have a use for it).

No joy.

[Vale!]

Well, no change I'm afraid.

The more I think about the CO2/acidification approach, the less I like it (for the application intended at least). I've abandoned my efforts so far.

So I'm going to try the 'several days of vigorous bubbling' method. I've set up a couple of airlines, with airstones because my 'bubbling' source mentioned that fine bubbles seem to help, in a 28-litre bin of RO/DI to which I've added the requisite amount of all the salts :

Sodium bicarbonate 5.37g
Calcium bleedin' sulphate 3.36g
Magnesium sulphate 3.36g
Potassium chloride 0.22g




I already know that everything else dissolves quickly, so I'll be able to track the dissolution of the calcium sulphate (switch off airline, let settle and assess any remaining sediment via a dip tube).

This amount, of 28L, will allow 4 x 10% water-changes. So I'll be doing this every month which is not what I was anticipating! I suppose I could make up 28L of just calcium sulphate at an elevated concentration and mix that with on-the-hoof preparations of the other three salts. That would increase the number of water-changes I'd get out of a barrel. But I'd need a mathematician to tell me how much calcium sulphate to add to it.

Iain and others : gird thy loins!

[Vale!]

This was a dip at the deepest part of the bin, and a dip from the middle after aeration had been stopped for a couple of hours :



Lots of bits of powder snowing around and a nice white carpet at the bottom of the glass. Sample returned and aeration back on.

By Grabthor's Hammer will I prevail.

[Gingerlove05]

I might need Grabthor’s hammer to prevail (great reference btw )
Ill keep watch for any mathematical equations that evade you