Nice to see some d.i.y builds going on, good luck...try not to use excessive amounts of media, you should only use the amount of media that you tank requires if not the bacteria will be spread thin across the media and your filtration will not be as effective,, which then means using the excess media you have put in your filter to start another tank will not work as you think it will,, you should only use the amount of media in your filtration that your tank requires,, your media will only ever have the amount of good bacteria on it that it needs for the amount of waste your fish are creating, so the more media you have the thinner that bacteria will be spread across your media, so you could end up taking handfuls of media out of your filter thinking that the media is ready to start a new tank and the media could have hardly any good bacteria on it as you have used to much media in your filtration, using to much media is not good,,