There is a rule stated by HDB with regards to tank size. Please refer to below website:
http://www.hdb.gov.sg/ISOA040p.nsf/0/fde4f...a5?OpenDocument
You can do a 7 feet but very troublesome... must apply permit from HDB
It says:
"The maximum weight of the total number of fish tanks (inclusive of water, sand and accessories) supported on a four-legged rack or cabinet must not exceed 600 kg per room."
HOW THEY MEASURE.... I REALLY WONDER MAN?!!!!?!?!
This is all thanks to the stoopid Luo Han craze lah when everyone starts putting a tank in their HDB flat... HDB scared too many people have too many fish tanks and the whole flat collapse lah...
BTW, I not from HDB