The following instructions are much like those in our DIY glass aquarium plans, but you are just taking an existing aquarium apart, rather than starting from scratch.
- Locate the section that needs repair and mark it, using some type of material that will not easily wipe off with water, i.e. a piece of masking tape, a felt tip marker that can be removed later with windex, etc.
- Remove all inhabitants, drain the tank, and remove the substrate.
- Rinse out and clean the tank with freshwater, then turn it upside down and allow the water to drain out and dry. You can wipe it out with a clean cotton cloth to speed drying if you desire.
- Relocate the section to be repaired and again mark the pane to be removed so you know which side of the glass is inside, outside, right, left, up and down, etc. This way when you reinstall it, it will be going back in the exact same way it came out!
- Take a razor blade and run it between the panes of glass to sever the silicone, and completely remove the pane. Be very careful and don't rush this step, and do not try to pry the glass pieces apart. Allow the razor blade to do the job, just 999working at it until the pieces separate pretty much on their own. Glass breaks very easily when pressure is put on it, and the edges can chip, making your repair job a much larger task if the glass gets damaged.
- After the pieces are separated, thoroughly scrape all the old silicone off with the razor blade, dry the joint areas, clean the surfaces with acetone, and allow all areas to dry for a few minutes.
- Cut 4 strips of duct tape, about 5 inches long, and stick them to anything close by within easy reach that has a clean surface to it, that the tape won't stick to too much, with at least half of the tape hanging down freely.
- Apply a thin but adequate solid line of silicone to the inside edge of the glass areas to be joined together, then, at a slight angle, place the piece onto the bottom base glass pane (in the exact way it was taken out), slowly tilting it upright and pressing it lightly, but firmly, down into the silicone.
- Secure the piece of glass from moving by taping it into place with two pieces of duct tape, each placed about 1/4 of the way from the top and the bottom, wrapping them around each corner from one side to the other. If you have trouble with the tape not sticking to the glass, just clean the area with some acetone on a paper towel and try again.
- Apply another solid line of silicone sealant along each of the inside glass joints, and run your thumb over the silicone from one end to the other of each seam to the smooth the silicone down and force it into the joint areas.
- Allow the silicone to cure for 24 hours.
- Refill the tank with freshwater and allow to sit about 12-24 hours. This gives you a good test period, and you will feel much more confident of success when you finally fill the tank with saltwater, put it all back together and add your inhabitants.
For replacing a broken pane of glass, remove the broken piece using the procedure in Step 5. Once removed, measure the piece carefully for proper precision fitting, then cut, or have a professional glazier cut a replacement piece. Ask the glazier to lightly smooth or buff the sharp edges, or you can do it yourself with a piece of emery cloth or silicone carbide sandpaper. Continue on from Step 6 to reinstall the new pane of glass.
That's all there is to it. Using these same instructions we even patched and restored a tank where the bottom pane of glass had completely broken in half, resulting in many continued years of use, but in our opinion it is best to replace broken glass altogether whenever possible.