Got me an Alkalinity question!
 

For the past while (I guess since about August when I really started watching it closely) I have been noticing my alkalinity dropping pretty quick. Historically I have found my tank to do best around dKH 9 and I prefer to keep it around there. I have found that my calcium stays pretty much constant between 420 and 460 ppm (changed a bit when I changed my salt mix) but my alkalinity will drop from 9 to 7 in about two days and will drop to about dKH 4 or 5 pretty quick after that if I don't do anything about it. So this leaves me adding carbonate fairly regularly.

What I am wondering is: is my alk dropping quick because it is being used up by my all my SPS or is there something else happening in my tank that is causing it to drop so quick?

I have suspicions that alk swings may have triggered an STN event this summer so I an trying to nip this and make it more stable.

My tank sits near a window and, up until the past week or so when it hit -9C, the window is open and gets decent air flow and it well aerated. The pH until the past few weeks has been on the lower side (7.8 to 8.1) but now sits around 8.2 to 8.4 (day/night).

Params:

Ammonia: 0 ppm
Nitrite: 0 ppm
Nitrate: <5 ppm
Phosphate: 0 ppm
Calc: 440 ppm
Alk: Wacky

Appreciate your input!

So is it a constant drop in alk, or is this a random thing. It sounds like you should set up a doser for carbonate. I was dosing sodium bicarbonate 20 times a day for stability. Alk swings=bad!

Typically, this is just normal usage of Ca/Alk. This is visible in dropping Alk due to the abundance of available Ca in general. The solution is to increase the Ca AND Alk additives to keep up with demand.

Ya, alk swings ='totally bad'. I found that one out first hand. What is blowinge away though is that alk plummets while calc is fairly stable. So it makes so wonder, is there something else that could be causing this rapid drop? If myy stuff is growing that fast, awesome! But I just am curious if it's something not awesome.

I have been debating a doser but I want to make sure that there isn't some underlying issue that I might be agrivating by constantly adding alk.

As long a it's a constant alk depletion rather than random swings cause by a precipitation event or something else weird you're good to go. SPS tanks always seem to use more alk than ca. Randy explains this in one of his articles, but I forget the reason :redface:

My calc remains fairly stable since I do frequent, moderate sized water changes and I've never found I've had to dose for Calc. If I get the tank to the levels I want, can I start dosing something like kalk to keep them steady or will I find that calc will build up with respect to my alk levels? I do have a bucket of Kalk that someone gave to me that I have been wanton to try but totally sure how to begin (I know the procedure, just unsure how it would affect the tank).

Thanks Rob! I'll look for that article/quote and post it up. I have't observed any major precipitation events so it's probably just uptake causing the drop in levels. I was just baffled that the alk would drop so fast compared to the calc.

its the same issue I have.. I can't keep ALK levels stable, and it is driving me crazy, I even have KALK set-up in the top-up water, but still can't keep ALK where I want it. CA & MG stay stable.

Hey, let's keep in touch. Let's see if we can't figure this one out together.

http://reefkeeping.com/issues/2002-0...ture/index.php

From this article:

"One of the interesting features of seawater is that there is a lot more calcium than there is alkalinity. By this I mean that if all of the calcium in seawater (410 ppm; 10.25 meq/L) were to be precipitated as calcium carbonate, it would use up a total alkalinity of 20.5 meq/L. In a less drastic scenario, let's say that calcium carbonate is formed from tank water starting with an alkalinity of 3 meq/L and that it is allowed to drop to 2 meq/L. How much has the calcium declined? It is surprising for many people to learn that the calcium would only drop by 20 ppm. Consequently, many aquarists observe that their calcium levels are relatively stable, but alkalinity can vary substantially. This is exactly what one would expect based on the fact that the tank already has an abundance of calcium."

Ahhhhhhhhh... gotcha! Makes sense. You know, being a chemical engineer, I should have sat done and done that math myself rather than... you know... being retarded. I shall keep up the baking soda dosing.

With kalk would you imagine that I'd still need to top up alk?

Thanks Rob!