Silicone Reseal
 

I was given a hex tank and as i was cleaning it i noticed that there is crud under the silicone...my question is can i cut away the silicone that seperated from the glass and reseal it like that or do i have to take all silicone off and make new seal...i put water in it and there are no leaks...been holding water for 24 hours already...the tank is about 20 gals. or so...

New silicone will not bond properly to old silicone, so you will have problems in the future. For peace of mind, I would strip it all down and reseal all of it. But that's just me.