Hello; I am unsure of the leak as you describe it. Leaks can be tricky to trace down. I have an old bubble up filter that drips onto the floor when the filter medium becomes clogged. I have to keep an eye on it. Some materials will wick water and cause a leak. I have had the surface film and bubble action cause water to work its way thru the plastic rim at the top of a tank and run down a corner making me think the tank was leaking. A bubbler can create a mist at the surface that throws water out of the tank or allows water to condense in places where it drips. (I like to position a bubbler so that the spray hits somewhere under the waterproof cover and drips back into the tank.) Of course, tanks and filters can develop leaks due to some structural problem.
I check a tank by sitting it up with only water in it. I try to dry the outside and try not to spill water on the outside when filling. Let it sit for a while and check for water on the outside. (A paper towel or dry wash cloth can be used as a telltale) It may leak right away or take a few days.
I have fixed leaks in tanks, but agree that it will best to exchange it for a new one if that is possible. I have found that trying to run a line of silicone only on a portion of a tank to not work out very well. 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. So, if possible take the tank back for an exchange or just but a new one. However for me there was always the need to figure out how to fix things and I will often spend more trying to solve a problem even if it is not practical.
I check a tank by sitting it up with only water in it. I try to dry the outside and try not to spill water on the outside when filling. Let it sit for a while and check for water on the outside. (A paper towel or dry wash cloth can be used as a telltale) It may leak right away or take a few days.
I have fixed leaks in tanks, but agree that it will best to exchange it for a new one if that is possible. I have found that trying to run a line of silicone only on a portion of a tank to not work out very well. 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. So, if possible take the tank back for an exchange or just but a new one. However for me there was always the need to figure out how to fix things and I will often spend more trying to solve a problem even if it is not practical.