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Thread: Tall acrylic aquarium

  1. #1
    DIYFK member nbrin's Avatar


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    Tall acrylic aquarium

    Hi All,

    Sorry for dragging this subject back, I'm pretty sure it has been somewhat discussed in past threads, but still wanted to confirm.

    I have been wanting a tall aquarium for ages, and finally I have the chance (space and money) to do one.

    I also have been wanting an acrylic aquarium for ages because the visuals are just amazing, however it seems that apart from scratching easily (or relatively easily compared to glass), there is also the issue of it being a less stiff material.

    I have an opening in a wall which will allow me to do a 1.6m (L) by 0.8m (W) by 1.1m (H). The roughly translate to 63 inches (L) by 31 inches (W) by 43 inches (H).

    Now for glass it is giving me 19mm, or 0.75 inches, however for acrylic it is giving me 35mm or 1.5 inches.

    The way I intend to build it is very much similar to how Joey built his cement 2000 gallon, but with fiber glass rather than cement, and the viewing panels will be back and front, not back and side. The acrylic will have an overlap of 2-3 inches all around with the fiber glass, and will be euro-braced at the top.

    Can someone please guide me to how accurate these calculators are, and whether the style which I am building it with helps to reduce the thickness.

    I know that a lot of you will say to go with thicker because its safer, but in reality, from experience, how necessary is it? Or shall I just go with low iron glass (I know it is not as good as acrylic, but at least it will come much cheaper)

    Thanks in advance

  2. #2
    DIYFK member Meep's Avatar


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    When you say 'fiberglass' you need to clarify how you plan to build this, you can't just substitute fiberglass for cement as fiberglass will bow and flex when cement stays rigid, thus an entirely different build concept as that bowing and flexing will cause all sorts of structure and sealing issues between the fiberglass and the acrylic or glass that won't be flexing and bowing at the same rate...

    As a general rule of thumb if you support the glass/acrylic on all 4 sides with a rigid 'frame' you can generally drop down one glass/acrylic thickness and still be safe...

  3. #3
    DIYFK member nbrin's Avatar


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    Yes you are right, the two materials have a different stiffness, and hence will bow differently under the same pressure.

    My intent was to build the main carcass using 4-5mm (3/16 of an inch) fiberglass (if needs be I will do it thicker). In terms of bracing, the idea was to manufacture the main carcass with a 5cm (2 inch) lip on top to act as a eurobrace, which increases rigidity same way it does to the top of an open bucket of water. Then at 1/3 intervals at the top I was going to do a transverse aluminium brace (so 2 in total), so that it will restrain it from bowing.

    As for the interface between the panel and the carcass I was planning to use silicone. Since it is relatively flexible, my thinking was that to a certain extent it would cater for the difference in "bowing" of the two materials, whilst holding everything in place.

    Hope that it is a bit clearer.

  4. #4
    DIYFK member Meep's Avatar


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    I personally doubt 3/16" thick fibreglass will be anywhere near strong enough for a 43" column of water...

    Your run of the mill fibreglass bathtub is give or take 1/4" thick and it's only holding 14" of water, I have no doubts that if you took measurements of a full and empty fiberglass bathing tub you would see probably at least a half inch of bow in the center, and that is only with 14" of water, 43" is an entirely other beast...

    A small fibreglass boat is usually no thinner than 1/2" and that is almost always curved surfaces with bridging, fibreglass over plywood or fibreglass sandwich with some type of structural core and what not to give it more stability but still allow it to flex...

    To put this into perspective, Joey's 2,000 gallon tank is give or take around the same depth as you want, and his walls are what? Maybe 6" or 7" thick of 5000 PSI steel reinforced concrete? I just can't see a traditional fibreglass layup doing the job without a lot of added support members, coring and ribbing... Sure fibreglass is strong but much of that strength is due to its ability to flex and give before it breaks, but in this instance, you don't want that flex and give as it's only going to complicate things and cause issues, cured silicone isn't flexible enough to take much flexing at all before it rips or the bond fails...

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    DIYFK member FLDave's Avatar


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    I'm "Old Fashioned" and would go with the glass.....Click here to enlarge

    I have one large acrylic tank and........would never buy another.....Click here to enlarge

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    DIYFK member h2so4hurts's Avatar


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    Agree with FLDave. Glass scratches, but Acrylic crazes. And there's nothing you can do for crazing other than stare at it and be pissed that it is there. At least with glass, if you're super careful, you can have a blemish free viewing pane for many years Click here to enlarge
    350G SPS/LPS Reef - Tomato Clown Pair, Maroon Clown, Sunburst Anthias, Powder Blue Tang, Royal Gramma, Desjardini Sailfin Tang, Whitecheeck Tang, Caribbean Queen Angelfish, Purple Tang

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    DIYFK member FLDave's Avatar


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    Click here to enlarge Originally Posted by h2so4hurts Click here to enlarge
    Agree with FLDave. Glass scratches, but Acrylic crazes. And there's nothing you can do for crazing other than stare at it and be pissed that it is there. At least with glass, if you're super careful, you can have a blemish free viewing pane for many years Click here to enlarge
    Acrylics also "bow" and, once that "bow" shows itself.....it's always there.....

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