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!)

 

[mfinn]

I am far from being a expert here. But I have built a few tanks (under 50 gallons) and attempted to reseal leakers.
I took a 120 that had a bottom leak and gave it the silicone treatment on the inside. I was pretty proud of myself until it developed a bigger leak a couple months down the road.
I've done the complete rebuild once on a 75.
That was pull the tank apart and clean the glass edges to make them like new. Then put them back together.
It took me more hours than it was worth it just to pull it apart. I swore, never again.

I had a 240 a few years ago that developed a slow leak on the bottom. One drip every 10 seconds or so. I did time it.
From what I knew at the time, this tank would be a good reptile tank. Not a fish tank.
So I advertised it as such. Free, just come get it.

A lady who I became good friends with came to me and asked to buy it.
She said many of her friends on Facebook told her she could fix it.
So I was desperate to get it out of my house so I gave it to her.

The people she had reseal ( interior only) were some pretty well respected reefers in the local community.
I thought maybe, just maybe..

About 4-5 months later I get a phone call from her at 6 am on a Sunday. She said water was pouring out of the bottom seam with a 6" wide stream. It was a complete disaster. Lost alot corals and fish.

I've seen this happen a couple other times.


So my opinion is you really need a fresh bead of good quality silicone between the pieces of glass. If it's already leaking, that very important bead of silicone is compromised and no amount of interior silicone is going to be a permanent fix.

 

[PotatoPig]

I am far from being a expert here. But I have built a few tanks (under 50 gallons) and attempted to reseal leakers.
I took a 120 that had a bottom leak and gave it the silicone treatment on the inside. I was pretty proud of myself until it developed a bigger leak a couple months down the road.
I've done the complete rebuild once on a 75.
That was pull the tank apart and clean the glass edges to make them like new. Then put them back together.
It took me more hours than it was worth it just to pull it apart. I swore, never again.

I had a 240 a few years ago that developed a slow leak on the bottom. One drip every 10 seconds or so. I did time it.
From what I knew at the time, this tank would be a good reptile tank. Not a fish tank.
So I advertised it as such. Free, just come get it.

A lady who I became good friends with came to me and asked to buy it.
She said many of her friends on Facebook told her she could fix it.
So I was desperate to get it out of my house so I gave it to her.

The people she had reseal ( interior only) were some pretty well respected reefers in the local community.
I thought maybe, just maybe..

About 4-5 months later I get a phone call from her at 6 am on a Sunday. She said water was pouring out of the bottom seam with a 6" wide stream. It was a complete disaster. Lost alot corals and fish.

I've seen this happen a couple other times.


So my opinion is you really need a fresh bead of good quality silicone between the pieces of glass. If it's already leaking, that very important bead of silicone is compromised and no amount of interior silicone is going to be a permanent fix.

For the 75 - how did this go long term?

I ask as someone somewhat near me has a 60” Marineland on marketplace, but it is advertised as having sprung a leak. My interest here is I have a 64” length of wall available to accommodate a tank so this would be amazingly ideal if I can pull it off…

 

[PotatoPig]

The silicone being replaced is the major difference


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!)

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 for taking the time to provide these detailed posts - it’s extremely helpful.

I’m still weighing up possibilities here - main one is an attempt to reseal a fairly large rimmed tank.

Would rimmed tanks be more forgiving / a better starting point than rimless?

And also, in terms of silicone- do you have any recommendations of specific vendors and products?

 

[exnisstech]

If you're getting a tank that is already leaking a rebuild would be the only option I would think. Resealing would be akin to putting a bandaid on a nicked and bleeding artery. JMO

 

[mfinn]

For the 75 - how did this go long term?

I ask as someone somewhat near me has a 60” Marineland on marketplace, but it is advertised as having sprung a leak. My interest here is I have a 64” length of wall available to accommodate a tank so this would be amazingly ideal if I can pull it off…

I had this tank in my dinning room for about 4 years before I sold it.
I didn't know the person who bought it ( craigslist) personally so I have no idea what happened to it.

I'm sure others will say different things on how to deal with it, but IMO, it would have to be completely taken apart and completely rebuilt.
This was a rimmed tank and it was a ***** getting the top and bottom rim off so it was re-used. When I was done there was a definite back side.
Sounds like that is the perfect tank for your spot.

I would check around and see if there are any others in your area that can help take it apart and then put it back together. 60" long pieces of glass are heavy and would not attempt to do it it myself, even 25-30 years ago.

 

[UncommonSense]

Would rimmed tanks be more forgiving / a better starting point than rimless?

This depends on the scope of the work:

Rimmed holds itself together better, but I’ve never personally gotten either plastic rim off even a 20g tank intact, so you ll be planning to buy new top and bottom rims from the likes of Over The Edge… (this means the tank must be pretty much exactly on dimension to even fit the new rims; 1/4” too big or small, and the rim will not fit on the tank!)

Rimless tanks are easier to cut apart, but are very unforgiving to mistakes during reassembly, and often have much thicker (thus heavier) panes… (my 5ft long reefer 450 [rimless] has front and rear panes which are .585” thick, and weight ~70lbs apiece, for context…)

main one is an attempt to reseal a fairly large rimmed tank.

Rimmed, or rimless; you don’t want to just slap some new interior silicone on a tank which does not reliably hold water. (Water damage in a home is absolutely brutal… wall framing often starts to grow mold, etc… it can be tens of thousands of dollars in damages)

— If you’re curious about a more robust solution that doesn’t entail a full tank rebuild, I am currently prototyping a glass reinforcement process without rebuilding on the aforementioned Reefer 450, dubbed The FrankenReefer 450

And also, in terms of silicone- do you have any recommendations of specific vendors and products?

Regarding silicones, I think you’ll have your best chance of success with the Momentive RTV100 series of silicones, vs. ASI aquarium silicone (or ASI 509, however they’re labeling them these days)… purely because the former has approximately 2x the workable time of the latter, lending itself to larger jobs!

Regarding suppliers, you want to go through one which really respects the expiration date on this stuff, and isn’t selling old stock! — last time I purchased Momentive RTV108, I went through a (surprisingly reasonably priced) aviation supplier, where I could specify within my order that I required a dead minimum of 12 months of remaining shelf life!

https://skygeek.com/rtv108-12c.html

 

[mfinn]

This depends on the scope of the work:

Rimmed holds itself together better, but I’ve never personally gotten either plastic rim off even a 20g tank intact, so you ll be planning to buy new top and bottom rims from the likes of Over The Edge… (this means the tank must be pretty much exactly on dimension to even fit the new rims; 1/4” too big or small, and the rim will not fit on the tank!)


https://skygeek.com/rtv108-12c.html

The 75 gallon tank I took apart had the plastic rim and I was able to get bottom and top off in mostly 1 piece each. Although required it's own rebuilding. Alot of superglue and some epoxy was used.
The tank if I remember correctly was a old Tropic Life tank. They were actually located not far from where I live in Olympia WA.
The rims were wood grain and much heavier than most others.
But like I said they needed fixing too.