do not use sand.. it acts as a buffer unless you buy a specific sand that does not raise ph, so becareful. either a mono or ocellaris, but honestly it is to small to id. oh and you should deff fatten him up a bit.. go to your local petshop and buy live black worms or live tubliflex and feed him that till he gains some mass and is large enough to eat those guppies. brine shrimp have no nutritional value unless you get vitamin enhanced so dont waist your time feeding the that unless you want to give them a treat.