Help me understand ALK

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stusclan

Aquarium Advice Activist
Joined
Nov 14, 2004
Messages
193
Location
phoenix arizona
Since adding my first coral (xenia) on Monday, I have upgraded my test kits. The LFS tried to explain why I needed to test for ALK instead of PH. This morning I tested my ALK and it was at 4.7. The upper limit is supposed to be 4.0. My PH was 8.0. I like to keep it at 8.2, but I'm not really concerned about that right now. What do I need to do to lower the ALK, and why is it more important than PH? I know how to raise my PH, but by raising the PH, am I messing up the ALK more - or helping it? I didn't test my CA or Phos. yet, didn't want to confuse myself any more. My amonia is 0, my nitraites are 0, and my nitrates are stable at just below 10. SG is 1.023. any help or further explanation would be greatly appreciated.
THANKS
 
Both are equally important and both should be tested.

Alkalinity is best kept withing NSW levels 1.5 -3 mEq/l. Personally I keep mine between 2.5-3 though. As far as your current level the easiest means of reducing it is a good sized water change with aged/aerated SW. Depending on your saltmix that should do the trick nicely. While 4.7 is on the high side, it's not at a dangerous level there's just no need for it.

As far as water chemistry is concerned, your tank (other than coralline) really has nothing in it that will deposit CaCO3 at any great rate. For now at least, water changes should maintain the necessary levels without the need for additions.

One thing that may be of concern here is having a pH of 8.0 with such a high alk level. This can be an indication of a CO2 problem. It depends on when you tested the pH. If early in the day then there is no need for concern. If late afternoon/evening, then I would look at how the tank is set up. pH related issues are often environmental, not chemical so additions are rarely if ever the way to solve it.

http://www.advancedaquarist.com/issues/may2002/chem.htm

Cheers
Steve
 
Alk reflects the capacity of the water to resist changes in Ph. The higher the ALK the less resistant your water will be to a swing in Ph. Corals like this stability. ALK in sea water is about 2.5meq/L, but in the home aquarium readings of 3.2-4.5 are more desireable. Again, the higher ALK will give you a more stable Ph. I would disagree with your LFS in that testing for Ph is not important. While Ph and Alk do work together, you should still keep an eye on both. HTH...Lando
 
Thanks guys, Steve, I tested first thing this morning - just when the lights went on. I do water changes every two weeks, so I'm due this week. I'll mix up my salt tonight and do the change Tuesday. The Xenia is happy and pulsing, so I guess everything is fine.

I really appreciate your help in explaining the chemistry stuff to me.
Terry
 
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