I can't think in mm or cm (assuming dimensions are cm), LOL. I think 5mm thick glass is only .19 inches. To me that seems very thin for a tank that large. I would think you want 1/2" glass minimum for that large of a tank which is about 13mm.But I haven't built my own tanks, so I could be wrong.
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Keith
"Simply put, you believe that things or people make you unhappy, but this is not accurate. You make yourself unhappy." Wayne Dyer