Vacuuming Planted Tanks
If you have planted tanks, you don't want to vacuum up the nutrients and potentially damage plant roots. However, small, planted tanks will require frequent water changes to keep the water pure enough for fish and the plants, but don't push the syphon into the substrate too far.
I leave a small area open in one corner of each of my tanks just large enough to accomodate the vacuum and then remove about half the old water and replace it with new, treated water of roughly the same temperature.
"Fear not my child, just change the tank water."