The gravel...

Years ago, the only gravel aquarists in India used was the white marble chip pieces which in time turned ugly green or brown. Then they moved on to sand, which tended to compact and was a pain to clean up. With Internet, snazzy pet shops and loads of aquarium books, things have changed for the better.

The choice of gravel or substrate that you want to use depends upon what you want to do with your aquarium. If you just like to see fish frolic in the water with an airstone and filter to clean up the poop, then you can go for fancy sand that has 7-9 mm rounded grains. Switch on the fluorescent tube and the sand begins to shimmer and shine. But, don't even think of plants if this sand is to your taste.

If you think plants, then you have to learn a bit of chemistry. True aquatic plants require nutrition and they draw it from water, but the chemistry of the substrate does affect the plant growth. The sand grains have to be big enough not to compact and small enough to let the roots grow. The sand is a neutral medium, plants need macro and micro nutrients. Only if these nutrients are made available the expensive plants that you buy from the pet shops will survive.

~S.N.