Experience Resealing Aquarium?

[PotatoPig]

I’m trying to set up a new system, and am sourcing from Facebook marketplace and Craigslist - I’ve seen a couple of tanks that are very cheap (or free..) that the seller is upfront that they have a leak.

Assuming a vaguely competent DIY person…

How difficult is it to reliably reseal an aquarium (size - 75-120 gallon)?

Also, and I’m seeing conflicting advice on this, do you need to seal *within* the joints, or do you “just” clean out the silicone from the corners, clean the glass with acetone, and then reseal without touching the joints themselves?

 

[Fish Fan]

Here's how I answer this:

I've resealed dozens of (standard, rimmed) tanks by scraping out the old silicon, carefully cleaning the glass, and carefully laying a new bead a silicon. I was told like 35 years ago, that if a tank was more than 10 years old, you should reseal it just out of an abundance of caution. This has worked very well for me, I've never had a tank reseal fail, and this includes a 125 gallon running almost 8 years after I did the resealing.

All that said, more recently I've been told by those in the know here at Reef2Reef that resealing like this is not a good idea. I've been told that the 'correct' thing to do is to completely separate and clean the glass panels and basically rebuild the tank from scratch, which is not easy to do if you're not setup for this kind of work.

@UncommonSense may have more info here

Best of luck whatever you decide!

 

[jackintheboxfish]

Here's how I answer this:

I've resealed dozens of (standard, rimmed) tanks by scraping out the old silicon, carefully cleaning the glass, and carefully laying a new bead a silicon. I was told like 35 years ago, that if a tank was more than 10 years old, you should reseal it just out of an abundance of caution. This has worked very well for me, I've never had a tank reseal fail, and this includes a 125 gallon running almost 8 years after I did the resealing.

All that said, more recently I've been told by those in the know here at Reef2Reef that resealing like this is not a good idea. I've been told that the 'correct' thing to do is to completely separate and clean the glass panels and basically rebuild the tank from scratch, which is not easy to do if you're not setup for this kind of work.

@UncommonSense may have more info here

Best of luck whatever you decide!

A little confused. What’s the difference between resealing like what you’ve been doing completely rebuild the tank?

 

[PotatoPig]

Here's how I answer this:

All that said, more recently I've been told by those in the know here at Reef2Reef that resealing like this is not a good idea. I've been told that the 'correct' thing to do is to completely separate and clean the glass panels and basically rebuild the tank from scratch, which is not easy to do if you're not setup for this kind of work.

@UncommonSense may have more info here

Best of luck whatever you decide!

Thank you - the tanks I’m looking at are all the standard framed tanks. I’m not quite bold enough yet to try a rimless tank…

 

[Fish Fan]

A little confused. What’s the difference between resealing like what you’ve been doing completely rebuild the tank?

I'm talking about a regular, plastic rimmed tank, and I've basically scraped and dug the silicon out of all the seams, cleaned it with acetone (uncommonSense does not suggest this!) or isopropyl alcohol, and reaplied the silicon and that's worked well for me for years; no failures at all.

I've since been told that you shouldn't do this. That you should completely take the take apart, separate all the glass panels, and remove all the old silicon and then basically rebuild the tank from five separate glass panels.

I'm not saying I'm right or wrong here, but I hope that made sense

 

[UncommonSense]

A little confused. What’s the difference between resealing like what you’ve been doing completely rebuild the tank?

The silicone being replaced is the major difference!

For context, the tank is primarily held together by the flat silicone film in the joints between each of the glass panes, with the silicone physically inside the tank being primarily there for cosmetics, and to protect the aforementioned structural glass:glass silicone from creeping algae and wanton glass scraping!



This said, the difference is as follows:

— reseal: cosmetic tank interior silicone removal/replacement only

— rebuild: breaking the tank down to perfectly clean glass panes, and reassemble using quality silicone


Obviously, the latter is the correct way to create a water seal in a glass box which holds dozens of gallons of saltwater inside one’s home!


It’s worth mentioning that the plastic rims actually do an incredible amount of heavy lifting for holding the tank together, but they aren’t perfect, and glass does bend where unsupported!



Notes about silicone performance:

— the RTV silicones common in glass aquarium construction will have various performance specifications, typically being strongest in lap shear, and tension… the weakest metric of every aquarium building silicone I’ve examined is “Peel”, as measured in Pounds Per-Inch (PPI)… 400-500PSI of lap shear strength isn’t uncommon, but seeing anything over 30PPI is rare outside a few brands… (this is to say that the cosmetic silicone inside the tank does not hold together well when the structural glass:glass silicone seam in an area is compromised, and the glass pane is allowed to bend from the water’s hydrostatic force, creating a peeling effect!)



(As you can probably imagine, a cosmetic reseal is out of the question for a rimless tank with a compromised structural seam, given that there’s no top/bottom one-piece rims to help hold it together!)

cleaned it with acetone (uncommonSense does not suggest this!)

I’ve managed to refine my advice on this topic after having done more research:

— acetone is more effective than isopropyl alcohol at removing the invisible ghost film of silicone residue on glass panes after initial silicone scraping…

however, the grade of acetone which is commonly available at local hardware stores in 2026 (technical grade) has quite a few impurities in it, and will absolutely leave a film of residue on the glass if left to evaporate off in place! (The bottle may say it’s pure acetone, but it’s closer to 95% purity)

— if possible, I recommend going to your local auto body supply/a good auto parts store, or a lab reagent supplier to get industrial (99%), or reagent (>99%) grade acetone, which will avoid adding any significant residues to the glass you’re scrubbing to a borderline OCD level of cleanliness!

— once you’re finished doing your initial cleaning and scrubbing with acetone, switch to the highest purity Isopropyl alcohol you can get (ideally >=99%), and clean all surfaces a final time with it!

 

[Fish Fan]

The silicone being replaced is the major difference!

For context, the tank is primarily held together by the flat silicone film in the joints between each of the glass panes, with the silicone physically inside the tank being primarily there for cosmetics, and to protect the aforementioned structural glass:glass silicone from creeping algae and wanton glass scraping!



This said, the difference is as follows:

— reseal: cosmetic tank interior silicone removal/replacement only

— rebuild: breaking the tank down to perfectly clean glass panes, and reassemble using quality silicone


Obviously, the latter is the correct way to create a water seal in a glass box which holds dozens of gallons of saltwater inside one’s home!


It’s worth mentioning that the plastic rims actually do an incredible amount of heavy lifting for holding the tank together, but they aren’t perfect, and glass does bend where unsupported!



Notes about silicone performance:

— the RTV silicones common in glass aquarium construction will have various performance specifications, typically being strongest in lap shear, and tension… the weakest metric of every aquarium building silicone I’ve examined is “Peel”, as measured in Pounds Per-Inch (PPI)… 400-500PSI of lap shear strength isn’t uncommon, but seeing anything over 30PPI is rare outside a few brands… (this is to say that the cosmetic silicone inside the tank does not hold together well when the structural glass:glass silicone seam in an area is compromised, and the glass pane is allowed to bend from the water’s hydrostatic force, creating a peeling effect!)



(As you can probably imagine, a cosmetic reseal is out of the question for a rimless tank with a compromised structural seam, given that there’s no top/bottom one-piece rims to help hold it together!)




I’ve managed to refine my advice on this topic after having done more research:

— acetone is more effective than isopropyl alcohol at removing the invisible ghost film of silicone residue on glass panes after initial silicone scraping…

however, the grade of acetone which is commonly available at local hardware stores in 2026 (technical grade) has quite a few impurities in it, and will absolutely leave a film of residue on the glass if left to evaporate off in place! (The bottle may say it’s pure acetone, but it’s closer to 95% purity)

— if possible, I recommend going to your local auto body supply/a good auto parts store, or a lab reagent supplier to get industrial (99%), or reagent (>99%) grade acetone, which will avoid adding any significant residues to the glass you’re scrubbing to a borderline OCD level of cleanliness!

— once you’re finished doing your initial cleaning and scrubbing with acetone, switch to the highest purity Isopropyl alcohol you can get (ideally >=99%), and clean all surfaces a final time with it!

Thank you, always very informative

 

[UncommonSense]

Thank you, always very informative

Of course!

Here’s a fun example of glass bending I recently discovered when cutting simple 1/8” sheet acrylic lids for my 40g breeder’s current FW quarantine setup:

This is a standard dimension Marineland 40B (no plastic top center brace, 36” span, 6mm [~1/4”] glass), it’s barely filled to the bottom lip of top rim, yet you can see how much the 36” spans are deflecting based off that squared sheet of acrylic… (3/16” total deflection!)