If you are staying at the east, u can try pasir ris farmway. Both ah bend and auntie shops are within the same pocket, directly opposite them, AquaEmpire also carry some stuffs for marine tank. After visted this 3 places, just take a 10 minutes walk to Iwarna.
You can give coralfarm and the famous shop at lim chu kang a miss cos they are not really into equipments.
Aquamarine at paya lebar also another place you can go but do take note tha they are moving soon! Heard that they will move back to jalan kayu area.
Madzpets will be a nice place to go see see look look and of cos make purchase if u wish to, the boss very friendly and willing to share his knowledge, although shop is no that big but cosy!