What I would do instead of the sand is use something like eco-complete in the pots, it is dark brown/black and will provide the plants with nutrition and if you want to take it a step further try adding CO2.
An easy (although not always a reliable way) of creating CO2 is to take a 2 liter soda bottle drill a hole in the cap just big enough to tightly squeeze an air line tube though, apply some silicone to seal. When dry (give it about a day) fill the bottle 1/4-1/3 of regular white sugar, fill bottle to within about 3 inches of the top of the bottle and add bakers yeast, cap off and run air line to a power head with an airline input.
The reason for the CO2 is that the plants grow quicker and stronger and will out compete algae that will try to grow on them if they grow too slowly. I use the above method with 3 bottles connected to a gang valve then to a powerhead on my 29.