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Silicone and tank longevity

Annie G

Thread starter
31 Jan 2022

I have a 4 foot Rena tank (freshwater) which I have owned for 20 years. It has 2 glass pieces across the top which run perpendicular to the long sides. The silicone on these has failed twice. I am not sure how much these are contributing to the integrity of the tank if at all.

My question is about the expected life of an aquarium. How long is the silicone joining the tank likely to last? Don’t want to appear paranoid but also don’t want dead fish and a flooded living room!

Hope someone can help.
Of the places that silicone is most likely to fail, that's got to be at the top of the list due to the changes in air and humidity, bright lights, and maintenance contact. If I buy a used tank with bracing like that then either the silicone has already failed or I will cut it out and redo the silicone myself. So 2 failures in 20 years does not surprise me in the slightest.

If the silicone fails while the tank is in use, you can clamp the front and back glass together gently - try to get it to the same dimension as when the brace was in place - while you clean up the old silicone and put new stuff in place. Nerve-wracking for sure but it can be done.
Thankyou MartyK for your reply.

We have succeeded in re-doing the silicone on the glass struts.

That aside, should I be worried about the condition of the silicone joining the actual tank together?
Has the tank been in use the whole time or off-and-on during that time? Storage can be harsh on the silicone with rodents, sunlight, and freezing temperatures doing the most damage, in my experience.

I would definitely inspect the inside seal to see if it pulls away from the glass at all. Use your fingers or a scraper/razor. If you don't feel or see any problem areas then hopefully you'll be doing a water test to confirm.
Hi MartyK

The tank has been filled with water and fish for the last 20 years. No leaks so far! Perhaps I am worrying over nothing. I haven’t noticed any issues with the internal silicone and I am always careful not to use a razor blade in the corners. Thanks for your advice and prompt reply.
I have two 4 foot 75 gal tanks in continuous use for over 30 years with no leak. My tanks have no central glass on top, so I wonder whether the central glass is structurally necessary for your tank or just there to hold the tank top. I also wonder whether aging silicone glass tank in continuous use can leak. Most failures I heard of are from dried out silicone in unused tank, off balance stand, or manufactures defects that typically leak within a short time.
I likewise have not heard of many failures when in continuous use. It's always tanks that have been in storage for a long while and the silicone 'dries out' for lack of a better term.

Thanks both of you for your re-assuring words.

tiger15 , I also don’t think that the glass across the tank is crucial to its integrity. They aren’t like a brace holding the tank together, if anything all that they will do is stop the sides from caving in ! It seems to me that they were placed there to prevent the light fitting from being accidentally dropped into the water (it used to have the T8 lights in a heavy holder).

I have added a photo of one of the glass struts. Apologies for the grubby appearance but I don’t want to clean it and risk it breaking again (they both broke away from the silicone overnight on previous occasions - the clown loaches were not impressed)

Does anyone else out there have a Rena tank with a similar construction?


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You could silicone a 20mm wide strip of glass directly under the brace.

Like this.
glass support.JPG
Your local glass shop would cut it for you and smooth the edges.

Blue bit. This would give the silicone on the x member less down force and support some of the weight.
Trouble is the tank would have to be dry to do it.
Aquariums with glass braces will have been designed specifically around that, braceless tanks need thicker glass in order not to bend in the middle. I would not remove these braces as the glass may be too thin to be structurally safe on its own
Hello and thankyou for your replies. I like the idea of the glass support for the brace. We did not have the option of taking the fish out when the brace was re- attached before. The water level could be lowered enough to do the repairs.

Hufsa, I have been trying to work out how thick the aquarium glass is. I thought it would be quite easy to do but the silicone in the corners is black (this is a tank from an age where the colour of silicone was not of any importance) and I think some of the thickness is in fact silicone. Probably a pair of callipers would provide the answer. I am fairly sure that is nowhere near the thickness of modern rimless tanks.
From what I know, if the tank has always contained water, it last longer. Keeping it dry reduces the life of the silicone although I have no idea to what extent. As for general life of a tank, 15 odd years is a good safe bet for a tank in use. 10 years if you are paranoid like me !! I have to replace mine next year. One tiny 30cm cube leaking in middle of the night several years ago was enough to make make paranoid about tank glass leakage and all that. It also killed off my entire collection of blue bolt shrimp :(