I use the same thing. Geo marine aragamax crushed coral. I heard about this from a local reefer. I have been using this for about 4 months and my tank is doing great! I know the argument againsts using this is that there may be some impurities. I guess it is a little bit of a gamble but may also have other trace elements not included in the "high grade" stuff.
I use KNOP KORALlith. This product is made specifically for use in reactors and 99% pure calcium carbonate with no phosphates. I was extremely pleased at the results when I went over to it (was using Geo marine aragamax before). I maintain a calcium level of 450 using a self built reactor and have 0 phosphates and other impurities. I highly recommend this product! You can get more info and also purchase the product from the following sites. http://www.petwarehouse.com/http://www.northcoastmarines.com/knop.htm
I use and recommend CaribSea ARM. It dissolves at a little higher pH and does not contain any phosphates. They have it on sale right now at www.reeffantic.com for $11.99 for 8 LBS.
