Is your resin perhaps a year or more old? Resin that has been sitting a while or has been stored in cold conditions can turn cloudy as the solids in it start to precipitate out. If your resin is in a plastic bottle you can easily see this happening. If your resin is in a metal can, you can't see it at all.

The cure is to heat up the resin so the ingredients can redissolve. Setting the container of (unmixed) resin in a bucket of very hot tap water for 15 minutes or more will do the trick. Stirring helps. When the resin is nice and warm it thins considerably, so you can shake the container to mix it, too. Let it stay very warm, and sit a while before using to allow the air bubbles to escape.

The hardener doesn't usually have this problem.

hope this helps.

PGJ