Hello all..
Tank repair... Easy to do, just as long as you take your time and do it properly.
You'll need these:
Silicone remover. I use this http
/www.ebay.co.uk/itm/EverBuild-Silicone-Eater-150ml-Silicone-Sealant-Remover-/320924300737?pt=LH_DefaultDomain_3&hash=item4ab89435c1 Most hardware stores carry this, or something similar.
Scourers. Something like this http
/www.ebay.co.uk/itm/20-LARGE-HEAVY-DUTY-CATERING-GALVANISED-SCOURER-BBQ-/190378111239?pt=UK_Kitchen_Accessories&hash=item2c536b7107 Your local pound shop will have something similar.. cheap! Go for the ones that look like metal swarf.
Caulking gun (for the silicone). Pound shop or Ebay e.g. http
/www.ebay.co.uk/itm/SKELETON-GUN-SILICONE-SEALANT-MASTIC-CAULK-APPLICATOR-310ml-and-400ml-/140731109314?pt=UK_Hand_Tools_Equipment&hash=item20c43a4fc2
Aquarium safe silicone. Try your local glaziers.. or ebay http
/www.ebay.co.uk/itm/Aquarium-Fish-Tank-Silicone-Sealant-Marine-Safe-Sealer-/110701413153?pt=UK_Crafts_Cardmaking_Scrapbooking_Glue_Tape_EH&var=&hash=item19c6518321
This stuff is pure silicone.. no additives or anti-fungal stuff which **will** kill your fish.
Screwdriver. Flat ended.
Plenty of old newspapers and paper towel.
Hobby knife.. a new blade is better!
Some latex gloves. Ebay, Pound shop or car care place... I think Asda sell them now.
Masking tape. You could use sellotape, at a pinch!
Pile of books or similar...You'll see why, later.
Before you begin, take some photos of the tank, or make a diagram. You need to record how the glass is assembled. i.e. which piece fits inside/ontop of the other etc.
The hardest bit is removing any plastic surrounds.. If this applies to you, just be very careful and take your time. Use a knife or small screwdriver to probe for and cut through any sealant holding the plastic to the glass.
Use the knife to cut through the silicone beads on the glass junctions. Be careful not to cut too deeply.. You don't want to scratch the glass.
You can pull off the excess when you've freed enough to get hold of.. You'll see what I mean when you get there..
A screwdriver helps here for "running bead removal". As before, you'll see what I mean when you get there.
Don't try and cut between the glass junctions. At best, you'll break your blade, at worst, you'll break/chip the glass.
When you have removed the easily accessible old silicone, cover the joints (inside the tank) with the silicone eater. Slap it on! nice and thick.
Now wait a few hours for it to work.. check it after this time, scraping any freed silicone away. Reapply more eater and wait a bit longer.
When you think that the eater has finished its work, place the tank on a **flat** surface and try **very gently** rocking one side of the tank.
You are looking for the developing weakness in the silicone seal. You will see it slightly stretching. Patience and gentleness is required now.. don't forget glass doesn't bend!
When the seals (looking at the edges of the glass now) start to go, they will probably go quite quickly.. be ready for this!!
Assuming that you have now successfully dismantled your tank, take each part in turn to the sink.. Use the scourer and plenty of water to remove **every** trace of silicone. This is very important. The new silicone will not stick to the old stuff. Ensure that all traces are removed, especially on the edges. You may need to use some more silicone eater if any of the old stuff is stubborn.
Wash off well and continue with the next piece.
Buy your glass.. If you can, take the one opposite the broken one (it will be exactly the same size) with you and ask the glazier for one of the same size.
depending on the exact thickness of the existing glass (depends on the age of the tank, older tanks may have imperial thickness glass). If the existing glass is (example only) 5.5mm (not a standard thickness), go to the next greater available thickness. Don't go thinner!.
If the tank glass edges are not going to be covered with an edging strip etc. then I'd get the edges of the new glass ground. (You can do this yourself..but be **very** careful. Newly cut glass is sharper than a razor blade..as you have already found out!)
To reassemble:
Wear latex gloves and put plenty of old newspapers down.
Ensure that each glass piece is totally dry and has **no** traces of silicone remaining.. Take your time checking.. this can make the difference between a successful repair and one that immediately fails (leaks!!).
Layout the glass on the floor (like an exploded view, if you know what I mean).
You will probably end up with silicone "fingerprints" and dribbles on the glass. Don't try and remove them while the silicone is "wet". Wait until it has cured and then remove it with your scourer and plenty of water.
Start by smearing a thin film of silicone on the edge of the glass that sits on the bottom piece (or on the edge of the bottom piece if the sides don't sit on the glass). Place it onto/next to the base, and support it with a pile of books etc.
Repeat with the next piece, only putting silicone on the **edges** of the glass.
Use a bit of tape to help hold the glass sides together. Repeat for the other two sides.
Now tape the sides together. Make sure the sides are aligned correctly before you proceed. Use enough tape to ensure that the sides are secure.
Next, you will be applying the beads.. I normally do the sides first. Run a bead of silicon from the bottom to the top. Try to be steady and even in the application.. This takes a little practice.
Smooth the bead with your finger (use a constant, gentle pressure and speed). Now proceed with the next bead... repeat until all 8 beads have been completed. Ensure that the bottom 4 corners are properly covered.. use a finger to ensure this.
You'll now need to leave the tank undisturbed for about 3 days... Wait until the acetic acid smell has dissipated. An electric fan can help here a little.
When you are happy that the silicone has cured properly, take the tank outside and place it on a flat surface. Fill with water and leave it for a couple of hours to check for leaks. If all is O.K. then pat yourself on the back...Well Done!!
Any questions then just yell!!
Let us know how you get on.
I hope that this helps!!
Bodge99.
Edited to clarify things slightly! (05/08/12)
it must be aquarium safe 
