I have posted this in another forum a while ago and some people find it useful. Maybe it is useful for you as well.
You may want to try out one of the following....
Rhodorsil V2 Glazing Silicone Bostik Findley
Construction 1200 Glazing Structural & General Purpose GE Silicones
The $15 jobbie is likely the selley one.. which is grossly expensive when compare to the better stuff mentioned on top there and I have been advised that it contains a or some elements which is doesnt make it as good as the stuff above..
I have resealed 4 tanks so far, all done by meself and I can give you some handy tips if this is your first time...
1) make sure you have plenty of space, dont skip on space otherwise you will regret it..
2) use plenty of masking tape (the second post at the end would give you the reason in using it)
3) when removing old sealant, glass safety blade handy to cut old sealants and a vacuum cleaner to suck it all out. Much cleaner
4) buy some cheap latex gloves from woolies or something (it could also be sold as food prep gloves, same thing). These will save the pain of trying to remove sealant from your hands later on
5) I use the iso alcohol called isocole? (the green dinosaur) they are the same thing but much cheaper than the piss bottle u get from bunnings
6) Use a generous amount of silicon, do not skim on this or it will come back and bite u in the ass
7) Give at least one week of cure time
The tank you are doing are much better than the biggest one I did (3ft/90cm lenght is the biggest and the last one I have done so far) and that use almost a full tube, so you will likely need two tube. Practice makes perfect, the 3 ft tank took me a grand total of 2 hours after I learned from past mistakes (all of which I have listed on top as tips).
Lastly have fun and make sure you take the time (except the part where you have to rip off the masking tape before the silicon skins) to do it properly the first time.