Ca/Alk question

[john1979]

Is it normal for my calcium to remain constant, but my Alk to need constant replenishing? I run Kalk in my top-off water, but almost every day I need to add some additional Alk to keep it around 9.0 dKH. My calcium is always 430-435, but my Alk will be 9.0 on Monday and down to 7.0 by Wednesday. I end up dosing with the Alk part of Randy' 2-part solution daily. I've tested the water with Hanna checkers, Saifert tests, and even brought it to the LFS - results are always the same.

I just want to make sure that this is normal, and not an indicator of some other problem. Is it typical to use Kalk and one part of a 2-part solution?

Thanks in advance for your help!

John

 

[Randy15]

How old is your tank?

 

[cardiffgiant]

I use kalk and typically have to add more of the alkalinity part than the calcium part.

 

[Triggercdog]

What is your magnesium level?

 

[skidoctor]

That's what happens to me. from what I've read, it is completely normal.

 

[tmz]

Yes, it's normal for alkalinty to deplete fasterthan calcium.

As calcium carbonate precipitation ( biotic or abiotic) occurs 50ppm (ie 2.8dkh) of carbonate alkalinity is used for every 20ppm of calcium. These are the exact proportions provided by kalk two part recipes or calcium reactor. The alk depletion is more obvious than the calcium since it's higher and there is less of it ,only about 150ppm vs 400ppm calcium. The calcium is being used but at a rate low enough that it may be hidden in testing noise and not be easily seen with a hobby grade test kit.

 

[Gary Majchrzak]

thank goodness you're here, Tom :thumbsup:

additionally: age of tank and magnesium levels are irrelevant to this question.. as is method of Ca/alk supplementation. (B-ionic users take note!)

 

[tmz]

Thanks Gary,

Further , for one time adjustments dosing one part or the other to raise alk or calcium is ok but unless things are way off it's better to keep dosing the balanced amount ,ie, 50ppm alk to 20ppm calcium in most cases. Otherwise , at some point you'll scratch your head and wonder why your calcium is low all of sudden. When that happens alk will rise as newly dosed amounts will be unused. Corals won't be able to calcify either. The whole system falls off.
This calculator is very helpful when doing adjustments if they are absolutely needed.:

http://home.comcast.net/~jdieck1/chem_calc3.html

Magnesium slows precipitation of calcium carbonate .As a magnesium ion takes the place of a calcium ion on some forming calcium carbonate crystals it poisons it as a calcium site effectively stopping it from growing . This would effect alkalinity and calcium consumption pretty much equally with just a bit of extra calcium left over from the spots where magniseium parked on the carbonate. It would not throw off the 50ppm to 20ppm consumption ratio noticeably.

 

[john1979]

Thanks everyone. I don't know what I'd do without this site and all of the collected knowledge available here.

 

[cardiffgiant]

Thanks everyone. I don't know what I'd do without this site and all of the collected knowledge available here.

I know what you mean. I've been doing this for a while, but I still had to read Tom's (tmz) post a couple of times to make sure that I wasn't missing anything, and I still learned something new.

We're fortunate to have some very knowledgeable folks on this board. I feel like I keep learning from the questions of others.