, if you cover your existing sand bed with new sand (depending on how old it is), you are going to smother to death whatever is living in it and possibly cause a spike. Different creatures live at different depths in the sand bed, and at the lower depths, there is only anaerobic bacteria. it's the only thing that lives in low oxygen zones.
Like the statements above, adding more sand will not consume uneaten foods. If you have uneaten food on the sand bed, you need to increase flow and cut back on feeding.
Nutrients, or lack of, is the key to algae eradication.