If you do this, start clipping a felt filter sock to the edge of your bucket and put the end of your hose through it. This way the ‘dirty’ water comes out detritus free! I use this trick for my tanks under 2 months old, so I can put mature water from my older tanks and make sure they’ve got good biodiversity in there. Also makes cycles much quicker, I can have a fully cycled QT in a week or less using water from my tank and rocks from the sumpThat's not a bad idea to just save some old water to put back in. Thanks!