I'm not trying to argue with you, and I think building your own custom tank is definitely cool, but my 5.5g measures about 40X21X26.5 cm. That's pretty close to the tank you built. It actually gives you 10cm more length with the same depth and only adds about 6cm in height. I highly doubt you'll need a more expensive light to penetrate 6cm of water. Of course, you may not be able to buy a 5.5 gal in australia for $8, or at all for that matter. Nonetheless, kudos to you for building your own tank. You should have no trouble growing any groundcover or whatever else you want to in that tank and I look forward to pictures.