This what I used to do when dosed kalk regularly through my ATO.

1. Get a 5 gallon bucket and fill it with RO\DI water.

2. Put 2-3 teaspoons per gallon of Kent Kalk (I assume any will work).

3. Mix it up really good, wait about an hour and mix it up again.

4. Wait at least 12 hours for everything to settle.

5. Open the valve on the bucket a fill up my ATO.

This would leave most of the powder (but not all) behind in the 5 gallon bucket. Then the ATO would drip it in via a float valve into my refugium. This worked for me before I got a calcium reactor.

Like Erik said, you do have to monitor your pH to make sure it doesn't get to high.

-David