so i got this filter with my tank from previous owner, he said it is a chlorine filter.... he said when he had the tank and all when he filled it all he ever used was this filter he never added anything in the water to dechlorinate ( i have seachem safe powder ) and love it.... but ive been using the filter when filling up the tank anyway but still do treat the tank with Safe... i havent got a clue how to open it to check the filter itself inside to see if it needs replacing or anything.. ive tried holding it and turning the top but i get nothing lol ... there isnt really any part number or model number on this thing.... any help would be great... and the previous owner had LOADS of money so im sure he spared no expense