Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
If you need to get deeper into the sand, and are using a gravel vac:
Hold the gravel vac at an angle so about half of the intake hole is still above the sand.
Also, if you are draining into a bucket, lift the bucket high enough to slow the flow. Then the suction is less, so less sand gets picked up.
Also, keep a hand wrapped around the outlet tubing, ready to pinch it off. This stops the flow so the sand can fall out of the intake tube.
Other than that, once the plant roots get going you should not need to vacuum the whole tank, just skim the surface of the sand between the plants.
Plant roots add oxygen to the substrate, and this encourages the decomposer organisms. The substrate will stay pretty clean where the plants are growing.