GE Silicone 1 Door and Window not the bath stuff.
The mold/mildew inhibtor stuff causes all kinds of damage to the fish depending on what you've got... Gill deterioration, Lateral line deterioration, Hole in the head deseaseand some others...Apparental in some species it inhibits vitamin absorption.
I've resealed 40-50+ tanks, all sizes. And yes I've had 3 leak out of all of them, I was rushing when it happened and they leaked as soon as I put water in. As far as the others go they never leaked, a couple have 30+ yrs on them too. Take your time, clean everything well & then clean it again. You shouldn't need to cut the silicone from between the two pieces of glass just whatever is sticking out. Use a widgit (razor blade holder and never apply alot of force (emergency rooms are expensive). Let dry for several hours to make sure the old silicone hasn't gone soft from the chemicals you cleaned it with.
jimk's tape idea is good, just a little tricky...You have to remove the tape before the silicone cures, so pull it at a 45degree angle like when you remove it after painting. Do it slow 'cause the silicone could get stringy.
Hey you think silicone is fun, try the pitch (asphalt/tar I think) that they used on the old metal framed tanks. It took a bottle of propane to do a 10g tank and you had to be careful you didn't overheat the
slate bottom. That an experience.
Good Luck.
Just waitin' on the pic's now...
Dr Joe
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