Where's my ALK going?

[hkgar]

On March 7 is was 6.3 and over the next 4 days I increased it to 8.0 on March 12, Today it is down to 6.9, Calcium was 420 on March 7 and 450 today.

The only thing I have in the tank is 1 Yellow Tang, 10 small (.5 inch) Asterea snails and 4 Tuxedo Urchins, and of course 200 lbs of live rock.

Why would Alk drop so much?

 

[mess7777]

gremlins....definitely.

Seriously though, what test are you using...how confident are you of it's accuracy?

Any algae growth? What is your Mg?

 

[hkgar]

Using the Hanna Checker for ALk. Siefert for Ca and Mag.

Mag is 1500 - too high. It was 1500 on the 3rd and I did a 10% water change on the 9th.

 

[rsaha]

Very odd that alk would go down and calcium up...

Do you have coralline growing?

 

[hkgar]

No, no coraline growing, but a lot of hair algae. The tank was set up on January 9

Do I remember seeing something about GFO reducing Alk?

 

[tvoydan]

How did you increase your ALK? What were you dosing? Baking soda?

I'm struggling with keeping my alk above 7. It was at 9 at one point. But I have a high bio load and quite a few corals.

 

[hkgar]

I dose with Randy's 2 part recipe one.

 

[tvoydan]

As you probably know, ALK is going to get consumed by coral growth and any biological processes going on in the tank that basically produce acid. You really don't have a large bio load or coral load...

Have you tested your PH regularly? Won't a high CO2 content in the house contribute to PH swings using up ALK?

 

[hkgar]

I am running an airstone through my CO2 scrubber into my sump to push out CO2. PH has been staying about 8.1 when the Alk was 8. It has been slowly coming down to 7.7. I monitor it with my APEX
PH over 7 days
http://www.reeftronics.net/graphns.php?probe=03&period=week&member=garyk

The downward spikes occur when I dose vinegar, which I started on March 4.

 

[disc1]

Have you tested your PH regularly? Won't a high CO2 content in the house contribute to PH swings using up ALK?

no. The action of CO2 produces carbonic acid. That acid lowers pH but leaves behind a bicarbonate ion. So the net effect of CO2 is to lower pH without any effect on alkalinity.

 

[hkgar]

Still can't figure it out. Ca has been 420 for the last week and and Alk drops every day. I am dosing Randy's part 2 recipe 1 4 ounces every day and it drops about .5 every day.

Still searching for ideas.

 

[kenny4128]

Not to steal a thread but I am having similar issues. I tested my alk today at 7 dkh and my calcium at 500+ I know these readings go hand in hand but need some advise. I do have a GHA issue on my Marco rock and the tank is about 2 weeks old. I added some pH up to increase my alk, should in stop doing this and let the system balance itself out or should I continue to monitor and dose?

 

[bertoni]

0.5 dKH per day corresponds to 2-3 ppm of calcium per day. It'll take a long time to see a change in the calcium level, even without water changes. Water changes might be enough to keep the level acceptable indefinitely.

 

[bertoni]

For the high-calcium situation, I would stop dosing any form of calcium, and just dose alkalinity to keep that level in the 7-11 dKH range.