The foam is perfect for growing large colonies of nitrifying bacteria. It’s what makes a sponge filter so good at biological filtration – the process of ammonia and nitrites being converted to nitrates. … With that said, bio balls are a larger media and will work best in a large sump or external filter.

How long does it take for bacteria to grow on bio balls?

As soon as you drop those Marine Pure Balls into your established tank the beneficial bacteria will start to colonize them. After three or four days you’ll have a healthy population growing on them, but you might want to wait at least a week for good measure.

Do bio balls need to be submerged?

It is also important to remember that bio balls are not meant to stay submerged underwater. They are designed for water to trickle over them so that beneficial bacteria stays wet while the tank water is aerated.