Using Cal and Alk at different rates...

[GOSKN5]

So I have a 120 gallon that is about 6 months old.. some of the corals are older from tank transfer (upgrades)

 

I started noticing alk consumption was picking up several months ago and I actually had an Alk drop and lost a few chalices...

 

So I started testing more and dosing consistently... I started off adding roughly 3ml Cal and 4ml alk.. this remained the same for about a month or so...

 

I added a few SPS that have started to encrust and grow... I skipped a week of testing and but still dosed... Tested last night and my alk had dropped significantly.. from around 10 to 8.6.. I dosed to raise it back.. Tested tonight and same drop... 10 to around 8.6..

 

My calcium didn't usage didn't increase.. still roughly dropping from 450 to 425 in a 25 hour time frame...

 

Does anything sound off? Mg tested at 1450...

 

So roughly adding 20ml of alk and only 5ml of calcium to keep my levels where I want em.. any thoughts??

 

Manually dosing, reef fusion 1&2...

[bbyatv]

This article from RHF might help?

 

When Do Calcium and Alkalinity Demand Not Exactly Balance?

 

http://reefkeeping.com/issues/2004-12/rhf/index.htm

 

Good Luck,

Bruce

[SirLord]

This is normal. Carbonate gets used up quickly in my tank too. Plus, it's more likely to precip out. 

[Origami]

The ideal ratio for consumption due to calcification is 20 ppm of calcium for every 2.8 dKH (or 1 meq/l) of alkalinity. Several factors can affect this. Some corals will use some magnesium to offset calcium consumption in percentages from 0% to 5% or so. Coralline algae will replace up to 5% of its calcium consumption with magnesium and this can lead to long term deviation from the ideal. Another factor is creation of organic acids in your tank which can use up some of the alkalinity. Finally, for tanks that are still cycling or tanks with nitrate problems, the consumption of alkalinity can be more than what the ideal would predict. That's because, chemically speaking, the conversion of nitrate to nitrogen gas re-introduces a unit of alkalinity back into the tank. If this step doesn't occur, it's like that unit was consumed, leading to increased alk usage.

 

In all likelihood, you're probably doing fine. Look for calcium to drop 20 ppm for a 2.8 dKH drop in alkalinity (or close to that) and, if that's what you see, all is normal.