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Old 04-13-2011, 11:15 PM   #1
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Broken bottom - Repair directions?

Heya all - new member here. I've been Googling this topic all day and I keep ending up here in the search results, so I figured I'd best join.

I used to be fairly heavy into aquaria but a career change about a decade ago forced me out. Times have changed and now my daughter is madly taken with aquaria, which is great.

She's moved up through her tanks over the last few years (with great success under my guidance) and currently has a healthy 20 gallon setup. But of course, she wants more.

Today, courtesy of a co-worker, I got a free 50 gallon setup with probably $100 worth of decorations, substrate, plant-gro top, etc etc. I'm pretty happy overall, and my daughter was over the top when I brought it home.

However, upon teardown for clean up we discovered that the bottom of the tank was broken. Since it had spent the last 2 years neglected and being pushed around from one spot to another, I guess this shouldn't be surprising.

I tore it down this evening and it currently sits upside down on my bench.

I've precisely measured the dimensions of the bottom panel and intend to call around for some replacement price quotes tomorrow. I'm not scared whatsoever of the replacement procedure based on everything I've gathered here and elsewhere..but I have a question.

I know that silicone will not stick to silicone...so how do I seal the bottom edges inside the tank? The silicone in the corners, of course, comes down the inside edges and meets at the bottom. Once I replace the bottom, at some point the new silicone (holding the new bottom glass in place) and the OLD silicone (holding the side panels together) will have to meet.

At this junction, what do I do? Use a heavy amount and careful blend the two, the new over top of the old? Should I somehow dovetail the two?

Basically, how do I accomplish a watertight seal here?

Also, I noticed that the plastic trim piece that was on the bottom of the tank was cracked at one edge where it sits flush with the short edge of the tank, on the side. Best as I can tell although the trim is designed to meet (and support) the BOTTOM pane of glass, it serves no purpose structurally for the side panes - is this a good assessment? Accordingly, cosmetics aside, it should be fine to rebuild the tank using these same trim pieces without fear of structural problems?

Any guidance appreciated here!


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Old 04-14-2011, 02:19 AM   #2
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Well, you've got two basic options here.

First, replacing the bottom. You'll want the bottom tempered ideally, as long as you're not planning on drilling it.  Now as to prepping the bottom, once the old glass is removed mainly consists of removing ALL of the old silicone from the bottom edges of the remaining four sides. Both the bottom edges and the inside bits that overlap up. And, assuming it's a standard size aquarium, I know that you can usually special order replacement trim pieces. Either a good LFS, or the manufacturers web site?

Now to re-assemble. You're going to actually be laying down two beads of silicone around the perimeter. The first one is placed on the bottom edges of the old side walls. I find having the tank upside down simplifies this. Then line up the new glass and set it on "top". After the silicone sets, flip the tank back to the upright position.

Get some plain masking tape, and lay it down along the bottom four edges about 1/2 inch in from the joint. Do this on both the new glass and on the four old panes bottom edge, leaving the gap between the glass joints and the edge of the tape borders. Now lay your second bead of silicone down along the inside edges. Smooth them out, and peel out the tape while the silicone is wet. Leaves a factory looking edge.

Flip the whole tank over again and silicone on the replacement bottom trim piece.

Give it 24hrs, and it should be good to go

Or the second option, and my personal favorite - buy a new tank. Just the tank alone at one of the box store shouldn't cost more than $50-$60 bucks. You get the manufacturers warranty, and you can still use everything else from the original donation set up!

Good luck, either way.

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Old 04-14-2011, 07:18 AM   #3
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if you go for the repair, be sure to remove all traces of old silicone with a razor blade, then if you can get hold of some clean the area with a silicone sealant remover. it's pretty easy to replace the bottom glass, I've done it a couple of times, just be sure the areas to be resealed are clean, when you come to filling and testing do it outside, 50 gallons is a lot of water on your lounge room carpet. Good Luck!!

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Old 04-14-2011, 09:17 AM   #4
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If it's the bottom pane, you can use a variety of materials. Aquariums used to have slate bottoms. You could even do plywood if you seal it with epoxy or some other resin.
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Old 04-14-2011, 09:43 AM   #5
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Aquariums had slate bottoms when the panes were not joined to each other but sat in a bed of putty. Attempting to mate glass with any other material in an all glass tank will surely lead to disaster.
You do not need tempered glass for the bottom piece. A bottom repair can be done by adding a piece to the the inside on top of the damaged piece. Removal and replacement is the best method. All the silicone inside the tank needs to be removed so you can reseal the entire tank after bottom replacement. I would recommend against using a silicone solvent as you would risk damaging the important silicone, which is between the panes.
So, the procedure would be to remove the inner fillet, and the bottom, clean it all well add the bottom piece and reseal the entire interior. The bottom trim is not necessary for structural integrity, but if you go without it, the tank should sit on styrofoam; I use 3/4" white styro. If you can get the glass for a reasonable price, this is a very worthwhile endeavor.
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