水槽 (suisō) means “fish tank” | MotiTan Japanese Dictionary

More examples

毎朝、水槽の水を替えます。mai asa sui sō no mizu o ka e ma su

I change the water in the fish tank every morning.

Focuses on water kept inside a defined container, often as a visible living space for fish.

アクアリウムakuariumu: A tank or display that contains aquatic life and may refer to the whole display.

水をためて魚などを飼育する容器。mizu o ta me te sakana na do o shi iku su ru yō ki

As a Sino-Japanese compound, 水槽 (suisō) is made from 水 (sui, "water") and 槽 (sō, "tub"), so its parts directly describe a water-holding container.

The phrase fish tank is especially common for a tank in a home, while aquarium has a broader use that includes public exhibits and the animals they contain.