Calling on the experts!! Alk...

[ctniners]

Ok, I have received great advice from this forum in the past....I am puzzled...

Let me first tell you.....I use Coralife salt...so is high in Calcium...

I have a nano tank and last week I got a great deal and bought 8 sps frags and 2 softies..just in case is relevant....

I have been having Alk issues from the biggining...I do 3 gal water change everyweek in an aquarium that holds 21 gal of total of water

so,....I thought that Cal and Alk were hand in hand....like the analogy that you have a bowl of marbles, blue are cal and red are Alk...if you add more blues, you take away reds and viceversa....so why is it that I can have a 6.5 dKH and a 440 of Calcium???...How can this be possible?(I do not have a magnesium test kit..but it shouldnt matter)...so....where is the dKH going?..I would understand if I had a 560 Cal....but even the calculator tells me that at 12 dKH I should have a 440 Calcium??....also my PH is at 8.4..even more puzzling.

by the way, I used the salifert for the Alk testing and I did it 3 times in a row.

Thank you for all your help

[rsuplido]

http://www.advancedaquarist.com/issues/nov2002/chem.htm

[Randy Holmes-Farley]

Forget the marble crap. We use real science here. :D

Are you adding an alkalinity supplement? If not, it is just being used up by corals and coralline algae and other organisms.

FWIW, it is also true that either your pH or your alkalinity measurements may be in error.

but even the calculator tells me that at 12 dKH I should have a 440 Calcium??

No, that is not how to interpret the calculator comments. Calcium and alkalinity are largely independent in most ways.

Water changes are not sufficient to maintain alkalinity unless there is essentially no demand. Even 10% water changes per day is not adequate in a decent reef tank:

Water Changes in Reef Aquaria
http://reefkeeping.com/issues/2005-10/rhf/index.php

Figure 23. Alkalinity as a function of time when performing very large daily water changes of 0% (no changes), 5%, 10%, 15% and 30% of the total volume EACH DAY. In this example, alkalinity is present at 4 meq/L (11 dKH) at the start and is depleted at a low rate of 0.2 meq/L per day.

http://reefkeeping.com/issues/2005-10/rhf/images/Figure23sm.GIF



Figure 24. Alkalinity as a function of time when performing very large daily water changes of 0% (no changes), 15%, 30% and 50% of the total volume EACH DAY. In this example, alkalinity is present at 4 meq/L (11 dKH) at the start and is depleted at a moderately high rate of 1 meq/L per day.


http://reefkeeping.com/issues/2005-10/rhf/images/Figure24sm.GIF