Is a sponge filter enough to keep the water crystal clear in my fish tank

Size of tank? What type of fish? Sponge filter is two types of filtering. Particulate and biological. If you don't overpopulate and don't keep"dirty" fish, you can achieve clear water with a sponge filter. You still need to perform regular water changes for your fish's health.

Sponge filters remove the large particles of waste that float around. Carbon helps with making it clearer. I also heard purigen helps.