Hello; I will attempt to repost portions of two posts that i put on another forum.
The used posts will follow.
If a tank leaks, I find it best to reseal all the corners at the same time. (In my experience the silicone needs to be applied in all corners while it is still tacky so that it will bond to itself at the apex of each side.) I also cut out the existing silicone with a utility knife from all corners before trying to seal with new stuff. (If the first application of new silicone does not seal the leak, I cut out all the silicone that I have just applied and seal the whole thing again.) I also find that the silicone tubes that fit in a caulking gun to be the most handy way to apply silicone. The tubes of silicone that you squeeze with your fingers are just too hard for me to control and I have not tried to use them in years. You can plug the end of a big tube of silicone with a nail or something round to keep it from curing too quickly, as you may need it again. (Note – When you cut the end of a silicone tube, make the first cut near the end so as to have a small opening. You can always cut off a little bit more if the bead of silicone is too small.) I had to seal a tank last summer that had sat empty for a lot of years, it took three tries.
Hello; It looks as you are going to attempt to seal a different tank. Some more pointers in addition to the ones in a previous post. I usually give a tank a good cleaning before applying the new silicone. I use a paste made from ordinary table salt (Without iodine) and a soft sponge. (Do not use a sponge or cloth that has been used with soap or chemicals.)(I have buckets and sponges that are used only for my tanks.)The salt paste does not scratch glass (be sure the sponge or cloth used to apply the paste with is not coarse enough to scratch the glass on its own and watch for bits of gravel that seem to jump into the salt paste.) and does a fair job at removing the deposits from the surface of the glass. (Letting the salt paste dry to a haze should desiccate most critters if you want to disinfect a diseased tank.)(Note- wetting the glass will soften up the deposits somewhat.) (Also for stubborn mineral deposits, a razor blade in a holder that gives a firm grip is useful. Use a shallow the angle on the blade and keep an eye on the corners of the blade. The corners sometimes get bent and will scratch a thin line. Rinse the salt paste out and let the tank dry well.
Once the tank is clean, I think it needs to be completely dry before applying a bead of new silicone. Dampness tends to hide in the very small seams and in the corners of a tank. I suspect that dampness prevents the silicone from bonding properly to a surface and may result in a leak in a good looking seam. (note- this is not real critical, but try to have the tank in a place where it can sit for a day once the silicone has been applied, so you do not have to move it until the stuff can cure some. I usually try to wait for two days before adding water to test it.) If you manage to lay down a decent bead of silicone try to resist poking at it in an attempt to smooth out a bump or irregular spot. I usually try to smooth out the glob where the corners meet at an apex. You may get away with wetting your finger tip lightly with water and gently touch it. (Water on the outside of a joint should not cause a problem if you use just enough to dampen the tip of the finger and not enough to drip off.)(Does it sound like fun yet?). You will want several paper towels or cloths handy to keep the silicone wiped from your fingers. It will get on everything if you don’t and is a real pain to clean off. If you use a cloth to wipe silicone the stuff does not come out, so do not use mom’s favorite towel
I think you posted that the plastic frame is loose on the bottom. Not had that particular issue myself, but would likely try to silicone that in place and let it cure a couple of days before attempting the recaulk on the inside of the tank. Other on this forum may have pointers they are willing to share with you.
If you happen to mess up and need to clean up a smear,( and find that the more you wipe it, the more it smears.) it may be easier to let the silicone set up so that it is no longer gooey. It can then be rubbed off with a cloth or your fingers.
