Tank Is Leaking

[snazy]

Hi all,
My tank started leaking this morning. The leak is from the top front corner where the glass is siliconed so I was able to stop the leak by draining a few inches of water.
 
Can anyone advise what's the easiest/safest way to repair with all the fish and plants inside. Can I just put more silicone on the outside on top of the old or that won't hold it?
The silicone is actually what holds the two glasses together and is about a cm thick black silicone as on the picture below. The leak is coming from the top corner and it's quite powerful if I fill the tank up.
 

 

[DrRob]

You'll need it properly dry for silicone to take. Is this at the front or back? Best way I know is to add an extra piece of glass as a patch.

 

[snazy]

That's on the side/front corner. The seam itself is on the side. Do you think I can't use only silicone to apply over the old one or should I use a glass piece?
 
I found a very interesting sealant that can be even used under water.  Here is a link with more info below. Does anyone know anything about it? There are youtube videos too if anyone wants to see how it's applied.  It's called CT1 sealant.
 
http/www.ct1ltd.co...s-with-ct1.html
 
Well CT1 is not a silicone sealant but unique hybrid polymer formulation that is able to stick onto wet surfaces even under water making it the perfect sealant for sealing fish ponds, CT1 contains no solvents and is 100% V.O.C free so will not contaminate the water extremely fish friendly. There have been occasions when the fish have nibbled at the cured CT1 sealant with no adverse effect but with so many species of fish we cannot say that for all species.

Just to add that emptying that tank and taking out the fish is next to impossible. It's heavily planted. The leak is from that top right corner on the picture from the seam itself, so I am trying to figure if I can fix it just by lowering the water level.