Are you able to take a photo to post on here so we can be sure which type of frog it is? If it is an African Dwarf Frog, then they really are supposed to be kept in little groups of 3 or more.
When that pet shop told you to half-fill you tank with water, to an extent they are kind of on the right track there but perhaps they thought you meant you had a normal pond frog in a tank LOL. Basically, these aquatic frogs need to be able to reach the surface to breath air but they are not great swimmers, so if you have a tallish tank of anything over 15" height, then the frog will struggle to reach the top. You might see it swim halfway, then struggle to go any further and float back to the bottom again.
If this is happening, then please do reduce your water level by a few inches (halfway is a bit extreme). The older they get the stronger their swimming becomes but to avoid putting stress on them, make life easy for them by reducing that water level a bit.
African Dwarf Frogs (ADFs) are fully aquatic frogs and do not sit outside of the tank water, like pond frogs. If they accidentally were to get out of the tank, their bodies dry out and they die. So make sure your tank lid is not left open.
Another point to mention is feeding. They are not quick to reach food like fish are. They take a while to sniff it out before lunging for it. If there are greedy fish in the tank it's likely the fish will get the food before the frog has a chance. So you might want to buy a turkey baster (or use tweezers) to place/squirt food directly in front of your frog (whilst the fish are busy feeding elsewhere).
Regards, Athena
