Your post makes it sound like you are planning to just drip the powdered pickling lime into the sump - please tell me that's not the case.
You need to mix the pickling lime with RO water to make limewater. Most people add around 1 teaspoon of kalk per gallon of water. Mix it really well, then let it settle for a couple of hours. When it settles, you will have the excess powder settled to the bottom, and a crust forming on the top. What you want to drip is the stuff in the middle. If you are using a simple gravity-fed drip system, you will need to make sure you are drawing the water from at least 1/2" or so above the bottom of the container, so you are not getting any of the concentrated kalk into your tank.
I've tried several ways of dripping kalk, and by far the easiest and most reliable is using a dosing pump. You can get refurbished medical peristalic pumps off EBay for under $100. Another place to check out is
www.reefdosing.com. That's where I bought mine, although they are a little more expensive than the EBay outfits (if you're like me and avoid EBay whenever possible).
Another thing to consider is using the "slurry" method, which is basically taking a small amount of kalk, mixing it in a glass of water, and just throwing it in your sump at once (preferably at night). If you do this, you have to use a pH meter, and make sure you use a dosage that won't raise your pH by more than .2 (i.e. 7.8 to 8.0). I used it for some time with good results, but since I had consistently low pH, I started dripping kalk instead, which can help with pH problems.
Like mikester said mix it about 1 teaspoon per gallon of water....if you have a lower calcium demand you may want to use a smaller amount of lime. Also you may want to add some magnesium to your tank if your coralline isn't doing well.
