Uneven Corners on Rimmed Tank - Trim Issue?

Hi everyone,

I came home today and noticed that my 75-gallon rimless aquarium suddenly started leaking as I was sitting on the couch next to it. The leak came from the corner/side of the tank, where the silicone that connects the two glass panels had separated. I quickly drained as much water as possible using an electric pump, a 17-gallon tote, and buckets, but about 20-35 gallons of water still escaped onto my wooden floor. The water leaked down through the ceiling and wall into my basement.

This isn’t the first time something like this has happened—my SunSun canister filter leaked about 10 gallons while I was away about 6 months ago, which also went through the floor into my basement. Thankfully, my stand seems fine, and I dried it off immediately with no visible damage (I had coated it with poly when I built it). Now I have my filters in a tote to prevent it.

I’ve now moved all my fish to a 30-gallon HDX tote, filled about 3/4 to minimize bowing. I’ve also removed all the sand, driftwood, and water from the tank. Upon inspection, I can clearly see the silicone has ripped apart, going down about halfway along the seam. I bought this tank used (I believe it’s a Deep Blue model), and based on the silicone, I suspect it was resealed at some point before I got it—the rest of the silicone looks very well-flushed.

I need some advice on what to do next. I’m planning on buying a new used tank from Facebook Marketplace that has a rim on both the top and bottom and is in excellent condition. I’m debating whether I should try to reseal this old tank myself, leak test it, and then either sell it or switch back.

For now, my fish in the tote have 5x the dose of Seachem Prime for nitrite, a heater, and an airstone. I also have my canister filters running separately with a heater and an airstone, and I’ve added Dr. Tim's ammonia to help the bacteria survive.

If I do get a new tank, would it be safe to place it in the same spot? I realize I might need to consult an engineer or contractor to assess, but I’d appreciate your thoughts. I’ve attached pictures of the tank, the damaged silicone, the basement ceiling, and the tote setup.

Thanks so much for any help!

You should be able to run the canister filter on the tote to keep the bacteria alive and the fish alive.

You can also put the lid on the tote to help stop it bowing. It might need tape to hold it in place. If you have a canister filter with hoses, you can cut a hole in the middle of the lid to put the hoses in and to feed the fish.

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If you buy a secondhand tank check the silicon.

Good silicon is soft and slightly squishy but firm.

Bad silicon is hard and usually brittle (pieces can sometimes be broken off) and not squishy. It usually turns cream or white in colour and sometimes has bubbles in it.

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If you want to repair the tank, you will need to remove the piece of glass, clean all the old silicon off it and apply new silicon. It's a relatively simple job but is difficult if you have support straps or only a really thin layer of silicon between the glass.

Use a single sided razorblade to cut through the old silicon and to scrape the old silicon off the glass. Wipe the glass down with something to clean it (I can't remember if we used mineral turps or alcohol), then wash it with soapy water and rinse well. Dry the glass and then apply a layer of silicon to the glass and use tape to hold the glass in place. Leave it to dry and cure for 1 week then fill it with water and hope it works.

The silicon should be for aquariums and glass and can be bought from any hardware store. The silicon container should have a picture of an aquarium on it or say its suitable for aquariums.

Do not use silicon designed for bathrooms because they usually have mould inhibitors in them that can poison the fish.

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What is the house made of?
If it's brick and concrete then it should be fine.
If it's wood it might be an issue.

However, the fact the water ran into the basement would suggest any timbers in the ceiling weren't sitting in water for any length of time and the water should evaporate off the surface quickly. This means the wood will be fine.

If the wood is left to soak up water then it can be an issue. Particle board or chip board is rubbish if wet but they normally use proper wood for roof timbers and they don't normally use particle or chip board for floors. So it should be ok but it's always good to get it checked by a professional. You might be able to call a structural engineer and get their opinion over the phone. It's probably ok because it's not a flood and the water ran down into the basement.

The staining on the plaster ceiling is only covering a small area, which would suggest there wasn't lots of water there. Unless you have insulation that absorbs water. You can leave it to dry for a month then paint a sealant over it followed by a top coat.

Quick update on my situation:

After some stress with my 75-gallon rimless tank leak, I picked up a new (used) rimmed 75-gallon tank today, likely a Marineland. I checked the silicone carefully, and it’s firm and slightly squishy—so, much better than my previous tank, where the silicone was hard and brittle. I plan to repair that old tank in the future, leak test it, and either sell it or switch back, depending on how things go.

New Tank and Stand Fit​

The new tank is just slightly different in size—it’s around 48.25 to 48.33 inches in length, whereas my old tank was 48.125 inches. My stand has a top plywood board that's exactly 48 inches, so the tank overhangs a tiny bit on each side and isn’t flush in two diagonal corners. Here’s some context:

• Stand Structure: The plywood top is flat and level, with side plywood frames extending down (not touching the floor) and screwed into the 2x4 frame.
• Overhang: The tank slightly extends over the plywood board but rests mainly on the rim, which is quite thick.
• No Flush Contact: The tank doesn’t sit perfectly flush at two corners, but everything is level.

I believe this setup should be fine, but I’d love any advice or reassurance before proceeding.

Next Steps​

Tomorrow, I’ll:

• Leak test the new tank
• Add my sand and aquascape
• If all goes well, transfer the fish tomorrow night

Additional Updates​

• My house is wood-framed, but since the water drained quickly into the basement, I’m optimistic there’s no lasting damage. I’ll paint over the ceiling stains in a month, as suggested.
• I’ve uploaded a video and photos of the tank setup, including the rim and stand fit, for reference.

If there is any gaps between the bottom of the aquarium and the stand, it can cause the tank to break. I would put a 1 to 2 inch thick piece of polystyrene foam under the tank (between tank and stand) to remove the unevenness.

The side of the plywood stand that is splitting concerns me unless it's decoration and not part of the frame supporting the tank. And the white stuff on the frame is interesting, it could be mould or dust

is the silicon in the new tank creamy white in colour or is that the light and camera?
It appears the bottom might have been resealed and has newer silicon compared tot he sides. The main area to check with silicon is between the glass (where it joins together). If that's clear and there are no bubbles, it should be good.

Hi! Here are some details to clear up any confusion about the stand from my earlier message:

1. Silicone:
   • I’ve always thought Marineland uses clear silicone along the bottom of their tanks and black on the sides. The bottom silicone appears clear in my video. The white areas on the frame are just reflections from the flash due to the gloss stain and polyurethane I applied on the wood.
   • For the silicone itself, what may look like "bubbles" actually appear more like silicone glue spots, not air bubbles.
2. Sand Particles:
   • The white specks visible on one side of the silicone are just small sand particles.
3. Foam:
   • Based on Marineland’s recommendation from their website, foam isn’t ideal under rimmed tanks (better suited for rimless). I am unsure if this is true however because I don't know how it works.
4. Stand Structure:
   • The stand has two plywood side panels screwed in opposite sides of the frame for decoration. These panels don’t touch the floor but almost do, which might be misleading in the video.
   • On top of the stand frame is a plywood board (48 inches), with the thickness of the side panels I mentioned and small gap extending the overall length slightly. This adds 1.5 inches to the stand's overall length. (49.5)
5. Tank Fit:
   • My tank’s length is about 48.25-48.33 inches, slightly extending over the plywood top onto the thick part of the side panels. In other words, the rim of the tank on the left and right sides rests on the thick part of these side panels minimally like in the video, which I'm unsure will be okay for support since they are just screwed onto the frame and don't even touch the floor.

I also uploaded an additional video showing the silicone more clearly. Hope this helps!

With rimmed tanks all that can and must be supported is theentrie bottom frame. The glass itself sits above the support for the rim. I have a number of frame support only stands. Even on a complete flat surface, only the rim will be supported. I built noth stands for my 150 and 125 and they are both supported by the narrow side of 2x4 lumber.


The above were bought used and are quite old, they each have a raised ID plaque on the lower right corner. I had not seen this before until I got them.

I would not be surprised it they are 30 or more years old. They did not leak when I first saw them filled nor since I put them into use. I am a big fan of AllGlass. They changed their name to Aqueon.


I have a few 16 gal. Rubbermaid Containers I use for temporary applications. I wrap duct tape several times around the container about 6 or 7 inches down from the top. I fill these containers close to the top of the tape. I have never had one give out.

Thanks for the input on rimmed tank support; that really helps clarify. I’ve attached some additional photos of a level across the stand’s length and width to show the current support. I also have composite shims in hand if needed, but based on what others with the same tank have shared, it might just be that the stand top isn’t perfectly level. Tomorrow, I’ll move the tank and recheck the leveling of the standtop itself.

I’ve also attached pictures showing the specific unevenness. Some who have experienced the same issue with the same tank suggested turning the tank upside down to rest on the opposite rim to see if the issue is with the rim or the stand itself. I’ll try that too to help narrow it down. Thanks again! (the yellow plastic level is width, wood is length, from different areas of the tank).

Ive checked the levelness of the stand and found that the rear corners, both on the left and right sides, were not level slightly, with the bubble just touching the line. I shimmed the back of the stand to make everything level, but unfortunately, this didn’t resolve the issue with the uneven corners. It seems like the tank’s trim or rim itself may be uneven, as shimming made no difference.

When I moved the tank to my completely flat dining table to measure the levelness of the stand, I noticed the same issue with the diagonal corners being uneven, further indicating the problem could be with the tank’s trim rather than the stand. I’ve read that some people have tried to level-rimmed tanks using MDF, cardboard, or plywood; however, my stand already has a plywood top. It’s strange because my previous 75-gallon tank didn’t have this issue and sat flush on the stand.

I’m concerned about adding water and potentially causing stress points due to the unevenness. Do you think the tank could handle the pressure on these corners, or should I consider further modifications?

1/2 to 1 inch thick polystyrene foam under the entire aquarium including the rim. Extend the foam out 1/2 inch from each side. The foam will compress and should fill the gaps without putting undue pressure on the glass.

The other option is putting thin bits of wood under the areas that aren't level.

Thanks a lot for your advice! I’m thinking of unscrewing the plywood on top and putting a layer of foam between it and the frame of the stand. Do you think that would give the tank enough stability and get rid of the uneveness?

I can definitely see how putting the foam between the top of the stand and tank would get rid of any unevenness. However, I’ve read that putting foam directly between the top of the stand and the tank can cause issues, like uneven pressure on the glass, but I’m not sure how that works/ if they are true since I don’t know much about how weight affects materials under pressure. Do you think using foam in that way would be safe?

We don't have tanks with frames in Australia. Our tanks are just glass rectangles and we put them on foam all the time.

Putting the foam between the frame and top of the stand won't help.

You could put some cardboard under the edges that are too high/ low. It isn't as thick as wood but compresses down and you won't need to use polystyrene foam sheets.

I think it should be fine as long as the surface of the stand is level. I contacted Marineland and they said that "It is normal for the tank to sit uneven until water is added. Once water is added, the tank will even out and lie flat"