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Tips and Tricks on re-sealing a tank?


Active Member
Founding Member
Nov 1, 2022
London, Ontario
Tank - 60" x 18" x 26" 120G Extra Tall (I would like to avoid buying new because I have the stand, equipment etc. ready for this tank, it's in great shape otherwise, and I am planning on upgrading a different tank with my available funds).

Started leaking ~ 1 month after setup. Currently planning on re-sealing it once the weather sets in for winter and my outdoor project are put on hold.

The tank is in great shape except the previous owner resealed it (held water just fine in their home) but they had it on a 48" long stand, with 6" overhanging each side. There was a 5/8" sheet of OSB under the entire tank, but after having a closer look (now that it's sitting on a proper, level stand I built) there is a 1/16" or so gap under the middle portion of the black trim, with the 2 end portions of the black trim touching the stand.

My thoughts here are that they resealed the tank on their sketchy stand setup, allowing the middle to bow. Once set, it was fine on their stand, but on my level stand, the middle was trying to straighten back out and the silicone gave way.

I was thinking of setting up the tank on a level surface, removing all the old silicon, weighing down the middle with a few hundred pounds, and then resealing. Would this hopefully reduce the strain on the center portion once I reseal it?

I will also place the tank on a yoga mat prior to filling it again to help aid in weight distribution if the black trim refuses to straighten back out when I am resealing it.

Any other tips and tricks?
So, my first piece of advice is not to do it. If you're going to do it, I would pay a professional to do it.

There, I said it. I just find it very risky especially on that size tank. You can have a Biblical flood on your hands.

OK Now that I gave you my PSA, here's a site I found that seems to walk through what I have read is the proper procedure: Should I Reseal My Aquarium? - Hackers' Reef

Use a professional sealant made specifically for this: Aquarium Silicone Sealant - American Sealants, Inc.

Good luck and please take pictures and post here. This can really benefit others.
Thanks for the PSA. I'm aware of the risks when it comes to resealing a tank, and I think its a risk I'm willing to take given my DIY abilities.

Absolutely I was planning on using the highest quality silicone I could find for use with aquariums.

Currently the tank is moved off the stand, and into a spare room in my basement where I will be the work. Now I just have to string together enough time to get the job done without rushing it.
Okay so an update:

I have decided to give it a go with resealing the inside only, not breaking down the whole tank. I've read countless threads, websites and blogs and have watched hours of YouTube videos. A common theme I have seen is the vast majority of people are saying to go ahead and strip / reseal the inside only, no worries, with one or two people saying it's not worth it.

I'm going to take my time, I have lots of experience working with a caulking gun, and I feel confident in tackling this project. If it leaks again, I'll be the first to admit defeat and will take full responsibility because doing this does pose a risk.... however... I have also seen brand new tanks fail after a very short lifespan, so there will always be inherent risk in aquaria.

Things taken care of as of now:

Tank is out of my living space, and ready to be cleaned up - It's also in a spot where I can leak test it without issues.
I went ahead and ordered ASI branded clear aquarium silicone sealant, only because for a little bit more money I have the reassurance that 1) its fish safe and 2) it's used in aquarium manufacturing / repairs and advertised as such.
I've also ordered a silicone removal tool that comes with shaping tools for a clean bead.
I also have a pack of razor blades and some iso alcohol and towels on standby for this project.

Lastly, I 100% plan on running a smart Wifi leak detector to alert me audibly and via my phone if the worst were to happen again. At least I can catch it earlier.

I'll update as I get farther along. Worst case, I wreck a tank that already sprung a leak, best case, I have a 120 gallon tank up and running again!
I bought a used 90 gallon cube. 30"x30"x24" from a salt water guy getting out of the hobby. Tank was in great shape except for all the coraline algae in between the silicone. I tore it down completely to all 5 pieces of glass and re sealed it. Took 3 tries. 1st one had air bubbles trapped inside the silicone. 2nd try I trusted my gut and it said nope. 3rd time was a success.
Used about 20 razor blades, a gallon or two of vinegar, acetone and scotch bright. It took about a week to completely remove every single piece of silicone. Lots and lots and lots of arm grease was involved. Once super clean and wiped down I used toothpicks to hold up each side a wee bit off of the bottom. Also did this on the sides. This way when the silicone is applied it can go into that small crack. Pull the tooth pick when your tube is close too it. Cut your tube rather larger so its easier to apply the bead. 1st and 2nd times I used painters tape but 3rd I did not. It seemed that when pulled back up minutes after caulking it would pull up the silicone a little. Have every thing needed to go because there is no turning back. Use plenty of gloves and a respirator with chemical cartridge. That smell is potent. It also lasts weeks upon weeks until the silicone has cured fully. I let sit for about 3 weeks. Oh bought cheap ebay 90 degree wood clamps to hold all corners together. Used Momentive RTV 108 clear adhesive.
Unfortunate news, I started scraping the silicone off the tank, and just as I was approaching the area in which I thought was where it leaked, I noticed a large gap forming between glass panels, with no new or old silicone in it. I went another few inches and there was a 1/4” gap of nothing between the panels, straight through to the bottom black trim.

I no longer think a simple reseal will do the trick, either buy new or tear the entire thing down.

I think I’ll see what kind of Boxing Day sales my LFS’s have to offer and order new…

Not a bad thing, just have to wait for it to come in now!