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  1. #1
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    350G Tank Repair-new bottom Help!

    I am fixing my 350G tank which has original (broken) bottom removed. I have located some 1/2" salvage glass which is 3/4" too short to use as a bottom with vertical sides of tank resting on bottom but could be cut so that it would fit INSIDE of the 4 assembled vertical sides.

    I have questions:
    1) Tank is made from 3/4" glass with centre brace on top. I am planning to use 1/2" float glass which will be sitting on 3/4" plywood braced at ends & 2 places towards the centre. Will this "hold water". (It's an OUTSIDE tank beside my front door.)
    2) In terms of structural strength, what would be the ideal amount of space to leave at the glass joint between the edge of the bottom pane & the sides of the vertical panes of glass?
    3) My plan is to set the bottom pane on a table & then set the 4 assembled sides around it. I will then squeeze the silicone (black?) into gap. (I will apply the "internal" silicone beads &, maybe, euro-bracing, later. Will this work or will I end up with air bubbles which will cause the structure to be weak? Or will I not be able to squeeze enough silicone into the gap (1/2" deep) & have to turn tank over & put in more from the other (bottom) side?
    4) I would put polyethelene plastic sheet on tabletop to stop silicone from adhering to table top while silicone is setting. Does silicone adhere to this? If so, what other material should I use to prevent this from happening?
    Thanks, everyone. I appreciate your input.

    ALSO, if there is anyone who is planning a custom tank construction then I may be able to secure you your glass at a good price. Let me know your preferred tank dimensions & I will reply as to availability & price.
    Both 1/2" & 3/8" (12 mil & 10 mil) salvage glass seems to be available. It appears to be in unscratched condition.

  2. #2
    Senior Member
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    First off the bottom pane takes the most pressure and it should be thinker then 1/2 inch. My 230 is 1/2 inch sides and 5/8 inch bottom.
    Second... I would not use "salvage" glass at this location. Old glass dose get brittle and the bottom is again taking a very heavy load.
    As for slipping the bottom up into the sides .. Yes it can be done this way. A lot of tanks with ONE PIECE molded bottom frames are done this way. If it was myself I would skirt the bottom with hardwood to prevent movement and I would use new glass for the job.
    Rob

  3. #3
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    Thanks #1 for your salty words. I would prefer to use 3/4" glass as you suggest & which was present before but can't find any as salvage. I figure that the braced plywood underlayment should compensate. Its not like it has to have the structural strength to go on a metal stand where it is only supported along the edge. Am I wrong about this?

    The price of 3/4" glass cut 30"x72" has been quoted to me at $500 plus tax. I don't really want to invest that much plus my labour to repair a tank which will be used outdoors 8 months of the year. And as I do not know the age of this tank it is possible that the salvage glass may not be any older than the existing glass. I hope you see where I am coming from.

    Anyway, do you know how much tolerance I should leave as space between the bottom edge & the sides? It seems to me that if I have too much space it will weaken that tank & yet I should have enough space so that the silicone can be squeezed through, yet, worst case, not make it so tight that the bottom piece will not "drop through" (since the glass cutter cannot shave a 1/16" off.)

  4. #4
    Senior Member reefmutt's Avatar
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    I think you really want a very thin layer of silicone- like 1 mm of space. You need just enough glue to stick without flexing too much. I'd also glue another 1/2 inch by 2 inch rim (this may be what you meant by eurobracing) around the inside bottom of the tank for added strength to compensate for what you are loosing by having only a 1/2 inch glued surface instead of the 3/4 that was there originally. You'll just have to go real slow and maybe have someone on the outside of the tank to watch as you apply the silicone to make sure it is going all the way through. I'd try to do it in one shot from one side or you'll end up with bubbles- which aren't the end of the world unless there are alot.There is industrial strength pure silicone that is stronger than black silicone- I'd suggest using it. I'm not sure of the name, but I'll try to find out if no one else knows.
    This is quite an ambitious little project...I hope you don't have a wife watching over your shoulder. I don't think she would want to know about the details of this tank repair- especially if its going into the living room or something.
    Matt.

    Old system torn down to make a playroom.. planning a 62x42x28 high

  5. #5
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    If your check any newly manufactured tank there is next to NO space between the contact points. Just enough to seal the pieces together in a leak proof fashion. the strength at the joint comes from that tight fit and the fillet of silicone that is inside the corners of the tank. As reefmut pointed out .. this is not a place to use anything but the highest quality made for aquariums silicone sealer. IMO the CGE "made for aquariums" silicone is the way to go. Being that the bottom is thinner take special care to make sure it is on the same plan as the bottom of all the sides. You will want the bottom to be in FULL contact with your plywood on the stand.
    Put the new bottom on a flat surface. set the tank on 2x2s over the bottom. Apply a healthy bead of silicone to the inside bottom edge of the tanks side panes. Use a 1/2 inch X 1/2 inch bead. Use enough pressure with the gun to make sure there is full contact with that first 1/2 inch of the glass. With the help of a friend or two lift one end of the tank off the 2x2s and lower it down over the bottom pane. repeat this at the other end. The tanks downward movement will shear the extra silicone out of the joint upward where you can then create the inside corner fillets. The joints will also be full.
    Rob

  6. #6
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    Jan 2004
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    how about multy laminated glass there is a place in montreal that mentioned it to me, to make a custom 350 g tank and i dont think it was that much and he garented it so he say's hope it help'sint: int:

  7. #7
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    Smile salty

    well, you'll have your work cut out for you.you can't just slip a preassembled tank[sides] over a bottom and silicone. theres a few reasons. 1.were there new silicone meets the old silicone in the corners will not bond and will fail in short time as theres amazing pressure there.2.you need to actually apply pressure on all vertical panels to squeeze against the bottom edges and have it held in place until dry. then you can go inside the tank and clean it up[squeezed out silicone] with a razor.3. then you can apply your inside seem silicone bead.4.It would be VERY hard to lift all that glass down over a bottom piece with chipping it as its super heavy!!. you'll have to disassemble that tank and redo it if you want it to hold. I can get you a better price on glass. I built my own 500g with a few trail and errors.

  8. #8
    Senior Member Fisherman's Avatar
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    Johnny I'm trying to talk my wife into letting me build a 250G

    how much for the glass? pm me =)

  9. #9
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    My synthesis of the information provided has left me with the impression that I might not be successful in replacing bottom glass by insetting into the sides because tolerances are too critical to ensure only a thin layer of silicone & there is no way of clamping the panes together during the curing period. While euro-bracing inside & fixing hardwood along the outside might achieve success I think I have decided to budget for appropriate size pane of standard thickness for this size of tank. I value all the advice that I received on this forum. Thanks all! for your time & very thoughful feedback on this subject. (Johnny-?$ for new glass.)

  10. #10
    Senior Member Fisherman's Avatar
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    Johnny has a connection threw a local company... because he bought a crap load of glass from them =)

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