[Lupin]

A lot can be said on the pros and cons between these two.
There's not much disadvantages with gravel.
For sand, one thing that can be a pain is that when they become compact, they create anaerobic spots. This alone produces much toxic gases thus killing the fish. You need to stir sand frequently to prevent compaction.

Brie is right about choosing substrate. If the gravel is sharp, then obviously your bottom dwelling fishes won't like it as their barbels get injured. Cories are the most vulnerable to this.

By the way, Brie,I have seen some freshwater stingrays in my two lfs but size is the problem. Even if I have to get another tank, this fish will still outgrow the tank.:roll: They are very rare and a few people can afford them.

 

[Lupin]

Thats neat, I've never seen them for sale. But you also live in the Philippines. There must be different fish there, right?

Brie, sorry for not answering this for a long time. I reread again and I saw your question.
In the Philippines, for aquaria, only carps and plecs can be seen. Actually the plecs are foreign species. They have invaded one marshland and 2 lakes already. The plec mentioned is a Hypostomus plecostomus. Let alone ripping fish nets and eating the local flora and fauna.:shock: Even the golden apple snails are foreign species. They are considered as pests as they eat plants and are commonly found in canals, rice paddies, etc.
Both species were introduced via the hobby of fish enthusiasts.

As for the stingrays, again, they are rarely for sale and are very expensive. One lfs wanted me to get that but I simply refused because the idea of getting it is bad as I don't have another tank and besides a large space tank is required.