Calcium and Alk

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In an attempt to stabilize my Ca & Alk, I started adding Kents Tech CB to my aquarium two days ago. The params on the day before I started were:

8/17/04
Ca= 300ppm
Alk= 14.7dKH
pH=8.0

Now, according to this article: http://www.advancedaquarist.com/issues/nov2002/chem.htm

I am in zone 3. Also in accordance with this artical I am adding the Ca part (Part A) of the two part additive.

Certain other calcium supplements may also be OK (such as just the calcium component of the two-part calcium and alkalinity additive systems), but you do not want to add any alkalinity. You CANNOT use limewater or a calcium carbonate/carbon dioxide reactor to correct this problem.

So, the results in two days of adding 10ml for the past two mornings are:

8/18/04
Ca= 320ppm
Alk= 13.1dKH
pH=8.0

8/19/04 (did a 5% water change)
Ca= 320ppm
Alk= 15.0dKH
pH=8.0

As you can see, Alk came down slightly, the shot up. Could that be due the 5% water change? Ca moved up slightly, but seems to have leveled. I will add another 10ml tomorrow morning (8/20) and test again tomorrow night.

Any thoughts on these readings?