I've been doing some PAGE gels recently on PCR products, and every so often the front gel comes out smeared (including the ladder). I'm using the same reagents and procedure. It's not my technique as the back gel is fine, and other people in the lab have tried doing it, with the same results. What could cause this problem in the ladder as well as the samples, on just the one gel? I'm thinking maybe there is a problem with the tank or the powerpack - perhaps the voltage is too high across the front gel on occasion? My manager says it could also be the time it takes to load, but it's only an intermittent problem, so I'm not convinced. There doesn't seem to be any pattern to it.