Calcium help

More reading from magazines that I want to share with everyone. If these are getting annoying, please let me know. Jon and the other chemists may be correcting me here but lets see how it goes.

First let me start off by saying that soft corals also use calcium to produce "spicules". They are the tiny structures that keep a soft coral standing upright. So basically everything in your tank uses calcium.

Another thing that I did not know is that your salinity must be at natural seawater (35ppt or 1.025 specific gravity) or Ca and Alkalinity readings will not be accurate. This is due to the fact that concentration of ions in your water will be skewed.

Limewater or kalkwasser:
1. contains Ca and hydroxide ions, the hydroxide ions react with carbon dioxide to create carbonate and bicarbonate which stabilizes your pH.
2. very cheap, can be purchased from LFS in Kalkwasser or Pickling Lime from grocery stores.
3. is known to precipitate phosphate out of seawater.
4. should be dripped because over adding can raise pH to 12
5. very caustic, DO NOT inhale or get on skin for long periods of time
6. mix 1-2 tsp to every gallon to be added to aquarium. Wait for several hours until residual powder has rested on the bottom of the container. Use liquid be means of a drip usually over night.
7. can react with atmosphere which will reduce Ca and alkalinity in solution. Use for only two days then make more.

Calcium Reactor:
1. high initial set up cost
2. mixes carbon dioxide with calcium carbonate to provide Ca and alkalinity in balanced proportions.
3. can be used with limewater drip to make sure that no extra carbon dioxide that gets into the tank causes damage
4. expect to spend a month or so tuning in your reactor
5. make sure you use an electronic monitoring device so that your pH doesn't get too low.
6. The solution in the first chamber should be around 6.5 pH
7. second chambers are used to buffer the water back up and to help with excess carbon dioxide

Two-part additives:
1. more expensive over time, but easier than a reactor for a smaller tank
2. don't mix together
3. other trace elements are in the solutions
Most people already know about these such as B-Ionic or Kent A&B solutions




Edited by Marcus

Salinity

"A word here about salinity: If the salinity is not at natural seawater levels (35ppt), the results you get from calcium and alkalinity kits will not be accurate because the concentration of ions in the water will be skewed. Always test the salinity of your system first with a properly calibrated hydrometer, refractometer or electronic meter."

From what I gather, your levels of Ca and Alkalinity in your tank may show up differently from a test kit if your salinity is not at 35ppt.

What do you think? Maybe I should have worded it differently.

I don't understand the whole ion thing as well as you do. So I don't have an opinion. The author is Randy Donowitz. I didn't mean to lead anyone astray when I first wrote about salinity. I tried to interperate it as best as I could, but I guess it didn't work. I used the word "readings" to try to make a point that it only what the test said, not what the level actually is. Oh well, please help me to understand it as well.

Sure. I just keep giving credit to the magazine so I won't get sued.

Yes that is the article.

Edited by Marcus

I did think of one more thing.  In many studies the intent is not to measure the amount of anything, but the difference in the amounts.  For instance we could say that reef A has four times more copper than reef B.  However reef A may have 4 times the salinty as reef B.  In this case the reef is NOT in a state of high copper levels, instead we term it hypersaline and say it is simply high on all solutes. 

In those studies (which are rare) the salinity is important and is reported. 

Adam

ps- this topic is very ironic since my next big study appears to be on trace metal levels in the Samoan waters. 

Adam, when do I get to go to Samoa with you?

Jon, don't apologize buddy. I wanted yours and other's opinions on this so we could all learn as a group. If a prominent magazine is posting incorrect information, then we need to know that its incorrect. Thanks for looking out for me and everyone else!

Jon and Marcus,

That is exactly my concern.  Now I also use EDTA every day, but I didn't know that it was common in our home based test kits.  Thanks.  Now I have to rethink. 
Here was my concern before.  What if our test kits are testing low?  What if we have lots of calcium but they are alreadyin incorporated in organics or in viruses and the like?  Your point makes me think the other way, what if our test kits are testing high?  What if the EDTA is falsly elevating the levels of AVAILABLE calcium.  Hmmmm. 

I do have a solution, what if we used our home test kits to test our water, and to also test water straight from a reef?  We couln't quantify anything (since the accuracy of the testing instrument is what we are checking) but we could qualify the calcium levels and see how differnt our water is from the reef water.  That would be sketchy but possibly useful.  I don't think we could prove anything is, but we could prove things that are not.

Adam

Samoa this summer (I hope) and yes I will need several people.  Samples will be collected but not tested on site.  They will be tested by mass spec once I return.  No particular reason for Samoa other than Spargur got me thinking about it and my local Samoan tour guide has impressed me recently.  Testing trace metals, Cu Fe Pb etc.

This is a very interesting topic.

Regarding calcium test kits.  I use a HACH test "kit".  Kit is in "" because it's more of a procedure then a kit.  Instead of counting drops, I titrate directly from a burret.  More accurate (and it makes me feel like a chemist). 

This is how the HACH kit works and how, I would hazard to guess, all calcium test kits work (at least the ones I've seen/used):

1. The sample is made alkaline (pH 12 to 13) by adding potassium hydroxide or sodium hydroxide (KOH or NaOH) to precipitate magnesium as magnesium hydroxide, Mg(OH)2.
2. An indicator is added that combines with any calcium to form a red color (or some other "calcium present color", red is most common).  This is ussually some colored looking salt or a drop of a colored solution.  In some hobby test kits the color indicator is combined with the chelate used in the next step.
3. A strong chelate is then titrated (dripped) into the test solution.  The most common is EDTA, but I suppose others might be used.  The chelate is a very very good scavenger of calcium.  It first grabs up all the calcium not associated with the color indicator used in step 2.  Then it starts pulling the calcium from the color indicator.  When all the calcium is extracted from the dye, the color changes from red to blue.  That is the endpoint, all the calcium in the solution has been sequestered by the EDTA.

That's it.  It's just a math problem from there. 

I suppose if the calcium is very strongly held by something, i.e. held covalently... chemically connected not just complexed with another ion/molecule, then the kit would not see it.  But I wouldn't think it would be available for coral growth either.  But I don't know... that's what research is for.  Not sure regarding the comparison of our tank water with actual reef water.  Most here add extra calcium and carbonates to enhance coral growth.  So it's not apples to apples... or did I missunderstand you're idea?

My kit is "more accurate" only because I'm doing the titration using a burret.  I can resolve the volume of EDTA titrated down to 0.01 ml... which is equilivant to 0.8 ppm Ca in the water.  That accuracy is not really needed though, imo.  There's also the inaccuracy of determining just when the endpoint (color change) is met.

Yes, I test my water at work.  But HACH does sell a kit:  http://www.hach.com/hc?L3NlYXJjaC5wcm9kdWN0L2ludm9rZXIkRGV0Y WlsL1ZlbmRvckNvZGU9SDIvUGFja2FnaW5nQ29kZT0xNDU3MDEvVmlldz1QU k9EVUNUX09WRVJWSUVXL1BSRVZJT1VTX0JSRUFEQ1JVTUJfSUQ9SENfU0VBU kNIX0tFWVdPUkQvU0VTU0lPTklEfEJrRXpUWHBCZDAxVVNUQk9SR016VGtOY WJtUlhWbnBrUld4TVZIYzlQVUV4Y0V4TlZBPT18

If I didn't have what I have at work, I'd use the Salifert kit.  It's resolution is at 10 ppm Ca.  Plenty good.  My father in law just bought a kit (Red Sea, I think) with resolution at 50 ppm per drop!  That's terrible imo.

I think every Aquarium Systems kit (not just calcium) use repackaged HACH chemicals.  Anyway, I've gone on too long... Marcus, I wouldn't buy the HACH, the salifert is cheaper.

Adam's GC-MS ICP is a much better machine .  Why buy cheap?