Often threads don't get answered in a matter of minutes. If you did something like you claimed you did, calling 911 is a better alternative than eating a fish water filter.
If you used it rectally, consuming activated charcoal by mouth would not do anything, at least, not quick enough. Your mouth and your anus are at two different ends of the digestive tract. To answer your question, I would not use fishtank supplies internally. You can buy activated charcoal for human use at a pharmacy, though they may have to special order it.
