I'll try to be fair to both sides here.
Pros of bio balls.
First off, these little guys are great for starting a tank, they help tons in the cycle by breaking down the more toxic ammonia and nitrites into the less toxic nitrates and keep the oxyegen high.
Bio balls offer more surface area than an equal amount of a replacement item like liverock.
They have far more ability to oxygenate the water than liverock.
The more oxegen supplied to the process results in a faster reaction capability of the filter to change the breakdown process.
The amount of surface area contained in bio balls supports a far greater amount of nitrifying bacteria, The amount of nitrifying bacteria in any system is dependent on two factors here. The amount of food supplied and the amount of surface area available. Due to the round shape with the little spikes these little balls have much to offer in surface area.
With maintanance; to repeat; With maintanance these bio balls have a lot to offer any wet/dry sump application. They are not a bomb waiting to go off, they are not nitrate factories anymore than any other mechanical filter.
Cons of bio balls.
The do tend to get dirty, therefore they will collect a certain amount of slime and junk on them. This leads to a nitrate buildup. In larger amounts the nitrates can lead to a problem, typically nitrates above say 30 ppm.
This initself is the cheif complant about them and the big con that everyone talks about.
One of the big reasons that people change or remove the bio balls is to go to a more natural type of filtration. The other is that they do not want to hassle with cleaning them.
Bio balls are not the only way to filter the water. Liverock will work in its place by upping the water level in the sump and using it much in the same way you would in the main tank. Others just replace them with liverock rubble and let the water splash over them, but in my opinion this is not as efficant as the bio balls. Also my opinion that if liverock rubble is used without raising the water level the rock itself will still get as dirty as any bioball and will need cleaning itself, but since I have not personally gone this route I can not speak from any experience on the liverock in the sump.
In the end it is the one who owns the system who must decide how or what method they will choose to filter the water. What ever the choice is the goal is the same, to achieve excellent water conditions.
Anyone with a reef tank or saltwater tank must have a method of removing nitrates. Some just feel safer without the bio balls
Hope that helps some, and I hope that I did justice to both sides.
Thomas
