Right now, I have a single tank with a fancy-tail goldfish, a mystery snail, and an African clawed frog. In the next month or so I plan on moving my ACF to his own tank and leaving the others where they are. Which substrate would be best for each of these tanks? I love sand, but I don't know if it would be good for my setup. And do you need any kind of special filter with sand? I don't really know what kind of filter I have, but it has a little pipe with slits it that sucks in the water. Is that okay for sand?