Dosing Kalkwasser

[TeamPlayer]

I've been doing some research on the benefits of adding kalkwasser to my RO/DI top off water, and it sounds like its the way to go. I currently have a 70gal main tank with a 15g sump and a 5 gal top-off resevoir. Top-off water is added to the sump by way of and electrical float swith and a small powerhead. My question is can I add Kalkwasser to my 5 gallons of top-off water and allow the float switch to dose it, or do I need a dedicated dosing setup?

 

[TeamPlayer]

Here is a picture of my sump/top-off set up if it helps.

 

[Sk8r]

Just mix in 2 level teaspoons per gallon of ro/di and let the dosing pump do it.

First 'set' your desired cal, alk, mg levels by hand-dosing regular supplements. Kalk does not easily raise levels, but is very good at maintaining them. It does not supplement mg at all. So you have to do that one always.

 

[osprey77]

dumb question but if it adds calc and alk how does it not raise those and just maintain. I've always wondered that, if you add cal how will it not raise levels.

 

[Randy Holmes-Farley]

if you add cal how will it not raise levels.

Here's the basis of that statement:

You cannot use it to boost calcium by any substantial amount because it will push alkalinity too high. A 100 ppm boost to calcium would try (and ultimately fail) to raise alkalinity by 5 meq/L (14 DKH). It will fail because calcium carbonate will precipitate before you get that high in alkalinity.

But it can be used to offset the decline in both calcium and alkalinity, and it could be used for small increases in calcium, or reasonably large increases in alkalinity if added slowly over time.

As you add limewater, pH rises. That pH rise increases demand in the tank for calcium and alkalinity. So as you add more limewater, you often do not get excessive alkalinity and calcium, but rather the demand rises to offset what you added.

 

[Randy Holmes-Farley]

can I add Kalkwasser to my 5 gallons of top-off water and allow the float switch to dose it, or do I need a dedicated dosing setup?

The answer depends entirely on how much limewater is dosed in what period of time. Some setups dose too much at once, and the tank or sump pH will get too high. Others work just fine.

Adding 1% of the sump volume will boost the pH in the sump by about 0.6 pH units, so adding that much at once is likely too much and will cause substantial local precipitation of calcium carbonate.

This article has a lot more info:

What Your Grandmother Never Told You About Lime
http://reefkeeping.com/issues/2005-01/rhf/index.htm

FWIW, if you want more discussion of limewater/kalkwasser setups, there are hundreds of such threads in the Reef Chemistry forum.