thanks for the advice but 10mm is too thick and expensive... besides, i already have my glass ready to be build... the only thing i need to do now is to cut my extra glass for braces, build up a stand and pray that it would go well...

if not, well the only choice i can think now is to reduce the depth of the water... i just hope it would not break in my first try...

thanks everyone guys... wish me luck... LOL

oh btw, one more thing... its about the silicon, once you open it do i need to empty the can? is it okay that it will seal itself? can i reuse it again?

All silicone (fish, bathroom etc) in the uk all comes in tubes that you screw a cone shape on the end and use a sealant gun. When i have finished using sealant for a job i unscrew the cone, put some clingfilm over the hole and screw the cone back on. The sealant in the cone goes off but the stuff left in the tube stays soft and usable. When i want to use the sealant again i just put a new cone on. However if you havent got a new cone just use a drill to empty the cone