To wash my fish tank, I bought kitchen sponges for 105 yen ($1.12 €0.86) at a 100 yen shop.
It includes 8 blocks of sponge.
This is made by plastic. Vivid color side has hard surface and light color side has soft surface. I use vivid color side (hard surface) to clean the fish tank.
If you want to know something, ask me please.