Bio Balls work best in a "wet/dry" type filter. The large spaces allows air to flow into the bioball thus feeding oxygen to the bacteria living on it...
Bio Balls will work in a submerged situation, but there are other forms of bio media that will offer far more surface area per cubic inch...
These same high surface aea medias (such as ceramic rings) are less effective in a wet dry situation, as the majority of the surface aera is internal and air is less likely to get into these tight pores. But again,. they will still work in a wet dry.
I do not agree that 'rings and stars' need to be preplaced every couple months, or even ever.
I strongly suggest we all use ample mechanical filtration prior to our bio media. When physical waste gets into our bio media our bio media needs to be cleaned. When cleaning bio media it is enevitable that some bacteria will be removed with the waste.
Also fine waste particles will clog up pores in the porous 'rings or stars' thus makign them less efficient.
Therefore if you properly (mechanically) filter the water prior to pushing it past your bio media, you will need to rinse the bio media very infrequently and will never need to replace it.
