Do you have an ugly old tank or a leaker? Or just one that you don’t think will hold water? I want to help you out with fixing this problem.
I will go through the steps you must follow to reline a tank and show you how to do it. I picked a real rough one up for free because of the shape it was in, and it took about 3 hours to reline it.
A 25 gallon tank resealed in several places with various materials including Mono caulking, and poorly done.
Here are the things you will need. Razor knife or utility knife blades, windex, paper towell, plastic scotchbrite pad/sponge, and depending on the size of the project either a squeeze tube or a caulking gun and a tube of aquarium safe silicone and a vacuum for removing the debris.
First you will want to clean the glass and remove any dirt etc. from the tank. After that you are ready to start removing the old silicone or what ever it is that was used. Place the edge of the blade against the glass at an angle and slide it under the silicone cutting toward the face that is butted against first. This will take several passes before you will reach the oposing glass. Next cut into the silicone from the other face; be careful not to cut into the joint between the two panels. When you have cut deep enough the silicone should come out in large lengths or pieces. If you make diagonal cuts in the bottom corners it is easier to clean them out.
Your tank at this point should resemble the photos above. Vacuum out the debris, clean the glass with glass cleaner (not the foaming spray as it leaves a residue), and you are ready to start taping.
Starting with the bottom, place pull tabs in each corner. Then place your tape approximately one quarter inch back from the joints all the way around.
Taping the aquarium sides
Next, tape the sides. Start with the verticle runs first so that when you pull the tape it will lift the bottom run as you go. After this is done trim out your corners.
The tank is now ready for re-sealing
Now you are ready for the new silicone. Cut the tip of the nozzle at approximately forty five degrees with a quarter inch opening. I apologize that is hard to see in this photo.
Lay a quarter inch bead all the way around.
Press it in and smooth it with your finger – working everything in until it is fairly even and smooth.
It is very important to remove the tape immediately after smoothing. Other wise you will have tape siliconed to your glass and have dificulty removing it.
And the finished result should look like this. Wait at least forty eight hours before filling.
One final note – if you accidently get silicone on the glass, leave it to cure for twenty four hours and it will peal off easily with a razor blade.
Source: Aquarticles.com (no longer available)