Soy Wax Candle Forum - Online resource for soy candle makers

I started making candles about a month ago. The first 5 candles that I made came out perfect. But since then I keep getting this grainy texture at the top of my candles when they have cooled. I haven't changed anything. I am still using the same box of wax that I started with and I do everything exactly the same. The candles smell good while burning and in general the candle looks good all but the very top. I don't know what else to try. I tried pouring at a cooler temp and it still does it. Can anyone help me.