kalk question

[turquoise]

Hi Randy,

Nice to see a reef chemistry forum!

I was wondering about Kalkwasser solutions. What would be an ideal Molarity/Molality for a Solution. As I understand it, Kalk is only slightly soluble in water...if so, knowing a specific Molarity/Molality would be a great way of getting the most out of the Kalk mix.

Thanks,

George.

[Randy Holmes-Farley]

Yes, it is only slightly soluble. At 25 deg C, a saturated solution contains about 0.0203 moles/L.

Many people use a saturated solution, but that is really only optimal if your tanks needs all of that (or more). Mine needs less, but seems to be in the minority.

Also, when I have used saturated limewater, I typically add substantially more than is necessary. The undissolved solids on the bottom help protect the solution from being degraded by CO2 entering the system and precipitating CaCO3. When this does happen, some of the solids dissolve and help maintain the concentration of Ca++ and OH-.

[Newreeflady]

Also, when I have used saturated limewater, I typically add substantially more than is necessary. The undissolved solids on the bottom help protect the solution from being degraded by CO2 entering the system and precipitating CaCO3. When this does happen, some of the solids dissolve and help maintain the concentration of Ca++ and OH-.


huh??? I am sorry, but I just don't understand. I am trying very hard to understand and read this several times. I am new to the hobby, in fact am just buying the components of my system. I am trying to get an understanding of kalk so I thought i'd come here and read a bit of the chem questions, this has me confused. What does that mean "the undissolved solids at the bottom help protect the solution from being degraded by co2 entering the system and precipitatin caco3"???

Also, in reading these posts I see you all are actually trying to evaporate as much water as possible, why? What does evaporation do for kalk? Is that just so that you can add more make up water with kalk therefore increasing calcium?

Thanks for shedding light on this for me:rolleyes:

Angela.

[Randy Holmes-Farley]

Angela:

<< Is that just so that you can add more make up water with kalk therefore increasing calcium? >>

Yes, that's exactly right. In my case it is unnecessary to boost evaporation because my calcium and alkalinity demand is not that great. For others, however, getting in as much as possible is important.

As to the "protection", I didn't make that very clear. By having undissolved solid calcium hydroxide on the bottom of the container, you can dissolve more calcium hydroxide from this solid if any leaves the system by precipitating with CO2 to form calcium carbonate. So it doesn't realyy protect it against precipitation. What it does is dissolve more whenever it becomes necessary to maintain saturation. So it protects the saturation.

I'm happy to explain further if necessary, but the confusion was probably just my poor choice of the word "protection".