Going to change from gravel to sand, in my 240 g tank the measurements are 6 feet long by 2 feet wide and 3 feet tall if needed. The sand im going to use is pool filter sand, it comes in 50 lb bags. The questions is would 2 bags be eneuff for the tank with a bed about 2 - 2.5 inches of sand ? any help would be appreciated thanks in advance