Deciding which carbon (GAC) filter to remove city Chloramine

I would like to remove chloramine from my city water for my hobby fish farm, requiring about 250 gallons of new water per week (about 12,000 gallons a year). And also for drinking water (10 gallons a week).

I was at first considering a Large 20" PENTEK Cartridge in a "Big Blue" canister.

Looking in to it further I am now considering a back washable carbon system.

I was wondering advantages and disadvantages between the two modes of carbon filtration?

Also there are many used water softener systems available here on craigslist. Can I convert those into backwashing carbon systems?

Backwashed is much better than a cartridge filter and over time, you'll spend less money.

Changing a control valve from a softener to filter can be done on some valves but you have to know what you are doing and how to do it.

Thank you.