Unfortunately, your CEL is most likely independent of the low coolant level.
You can go to AutoZone and they'll pull the codes for you, or you can buy a generic code scanner - I have an Actron 9125 scanner which retails for $70, but I found mine for $50 on Amazon -
http://www.actron.com/product_detail.php?pid=16298 .
The coolant leak has been covered pretty well, my guess is a cracked reservoir (tank), but it could be any of the other things mentioned.