ChrisP

Hi Warren Glad to hear you're better. Been away, hence the delay in response. The question was whether a 120cm x 50cm x 75 cm deep aquarium made out of 10mm float glass (as per the GARF calculator) filled to 60 cm deep could withstand the (hopefully unlikely) eventuality of being filled to to the full 75cm depth in the event of an outflow blockage (filling to this height could accommodate all the contents of the sump). This, if you like, is my minimun safety factor. If it couldn't, would 10mm toughened (safety) glass resist this extra depth, recognising the risk of catastrophic failure if struck a violent blow? And lastly, what about laminated glass - could this combine the best of both worlds, or would it significantly reduce visibility (particularly if going for Starbrite/Optiwhite glass? Or do I have to bite the bullet and go for 12 mm float glass (or - gulp - Optiwhite) and accept the significant cost and visibility penalties over 10mm float glass? Many thanks, Chris

Thank you all for the advice. Just to clarify a couple of points. The reason for my confusion is when you enter this tank's dimensions (and I am entering water depth - 600mm - not glass height - 750mm) into the GARF tank calculator (http://www.garf.org/tank/BuildTank.asp), it gives you a recommended glass thicknesss of 3/8" (10mm) for all four sides plus base. With bracing around all top edges, but no brace across the centre. When you enter the dimensions into Warren's full equation (http://www.fnzas.org.nz/glassthickness.0.html), you get a recommended glass thickness of 12mm for the sides and 15mm for the base. HUGE difference in cost (and significant difference in viewing clarity). So I thought it might be because Warren was assuming there would be no bracing. But Pies has spoken to the man himself, and says there's bracing all around plus across the centre. BTW, if you use Warren's Excel spreadsheet to do the calculation for you (http://www.fnzas.org.nz/uploads/media/G ... sCE_02.xls), it gives you 12mm for all glass sheets. I guess this is all down to safety factors, but since I have no idea what safety factor I should set, I remain totally confused! 10mm all round? 10mm for the sides, 12 mm for the base? 12 mm all round? 12mm for the sides, 15mm for the base? And just in case this changes anyone's recommendations, there will be a wooden frame (12mm thick by 33mm high) sitting on top of the glass with 6mm thick MDF panels screwed/glued to the frame and jutting down 150mm around all four sides. This is for cosmetic reasons (to conceal the air space at the top of the tank), but if it is a snug fit around the glass, it should provide some extra stiffening. The second point of clarification is about toughened glass. I have used a lot of it for glass doors, shelves, etc., and like Daniel and Matthew, I have found it to be incredibly strong (i.e. both stiffer and more resistant to breakage than ordinary glass), but very prone to little pieces breaking off the edges if struck on the edge. If you do manage to hit it REALLY hard on the face, it breaks into a thousand pieces - instantly (there is NO in between - either it is completely unaffected, or it completely disintegrates). Never having used it in aquaria, I was wondering whether that extra stiffness would reduce bowing and hence the need for bracing, but I have no idea how it behaves under contant pressure. Any more views? Chris

I have used Warren Stillwell's glass calculator to calculate glass thickness for my planned 1208mm/48 in(long) by 500mm/21 in (wide) by 750mm/30 in (high) aquarium (BUT it will only be filled to 600mm/24 in depth - remaining clearance for overflow, space between canopy lights and surface, etc.). It gives me a thickness of 12mm (1/2 in) for the sides, and 15mm (5/8 in) for the base. I assumed that was without braces. But in talking to my LFS, they insist you cannot build a 4ft tank without bracing all around it and across its centre (using 2 in wide glass strips of the same thickness - 1/2 in - as the sides). Does anyone know whether Stillwell's calculations assume braces or no braces? Is it possible to construct a 4ft by 21 in all-glass aquarium, filled with 2 ft of water, without any bracing at all? Or at least, without a centre brace? And what glass thickness would I need to avoid braces (I know this will be a more expensive option, but I just hate braces!)? Lastly, in constructing the tank, should I use standard float glass or toughened (safety) glass? The latter is stronger, but shatters into a thousand pieces if struck hard, whilst standard float is more likely to crack (giving time to siphon out water & relocate at least some livestock). Many thanks in advance for your help.