from the sounds of the description you gave it sounds like you have an aquaclear filter. Click here and take a look and see if that's what you have. 
If that is the brand you have then it would help to figure out what model it is. If you can, take a tape measure and measure the dimensions of the filter. IMO, even 2 of the largest aquaclear filters (110 or formerly called 500) are not enough filtration for a normally stocked 155 gallon tank. that's why it's taking so long for the murkiness to clear. if you added one or even two more then the tank should be crystal clear all the time. At Big Al's online you can buy the largest model of Aquaclear (the 110) for $38. Also, some people have said that in their areas if you print out that page from bigals with the price on it that Petsmart may price match. then you won't have to wait for the filter to arrive through the mail.
as for the carbon, yes once the water has cleared up you'll be fine in removing it.
If that is the brand you have then it would help to figure out what model it is. If you can, take a tape measure and measure the dimensions of the filter. IMO, even 2 of the largest aquaclear filters (110 or formerly called 500) are not enough filtration for a normally stocked 155 gallon tank. that's why it's taking so long for the murkiness to clear. if you added one or even two more then the tank should be crystal clear all the time. At Big Al's online you can buy the largest model of Aquaclear (the 110) for $38. Also, some people have said that in their areas if you print out that page from bigals with the price on it that Petsmart may price match. then you won't have to wait for the filter to arrive through the mail. as for the carbon, yes once the water has cleared up you'll be fine in removing it.
most of the time employees at chain stores go by what's on the box, and on the box of the AC 110 it does say that they're "suitable" for tanks up to 110 gallons. however, a single AC 110 on a 110 gallon tank is less than half the filtration I'd want on the tank. IMO most tanks will do best with filtration to turn the water over 10 times per hour so on your tank you'd need 1,550 gallons per hour of filtration. that comes out to 3 Aquaclear 110's if that's the kind of filter you want to go with. 