stick with the charcoal  no it won't harm your fish if you put it down in your tank water  I got two end's of panty hose's with charcoal & tie the top's & snip half thee excess panty hose top's leaveing just a lil bit to grab  & I putted  1 in each corner in my tank & my 3 fishies have been doing fine there healthy as can be but make sure rinse the panty hoses that has charcoal it elimnates any dust in the charcoal then ya put the panty hose charcoal filled down in your tank & then  woohlllaa!!! your all set  you wanna change the panty filled hose of charcoal every 2 or 3 week's. woohlllaa!!! there ya have it your all set .