How to clean or replace bio-filter media?

[pingapple]

I have a 10 gallon tank with a simple overhead filter box on it, keeping 1 angelfish. The tank has been running for a year.

There are two layers of filter wool in the filter box. If I replace one layer of them with new one, will there be enough bio-bacteria to do good nitrification? Any experience in doing that? Do you think any difference for replacing the top layer or the bottom layer?

Some local fish shops use 1 or 2 simple filter boxes to keep lots of fish in a 5 gallong tank.

I have the following guess. Not sure whether they are correct.
(1) A small surface area is enough for a lot of nitrification bacteria to grow on it.
(2) Bacteria can survive with very small amount of ammonia and nitrite.
(3) Bacteria can nitritfy a huge amount of toxic comparing to the little quantity which can keep them barely surive. (Analogue: bateria can survive with one mouth of rice but it can eat 10 bowls of rice without problem)
(4) For a sessioned tank, taking away half of the bacteria in a tank, the other half can still do the nitrification with double the time duration. That will still be a very short time for a tank with normal load and a simple filter box.

[admael]

Fish stores have their tanks overstocked because it's only a temporary solution, they expect to sell the fish.

Replacing half the bio media should by fine.

[v_nod]

If the flowrate of the filter has not decreased, why fix something that is not broken? But if you do want to change, half of the sponge is fine. Or you can wash the half in old tank water. I keep an overhead filter as well, you might want to add in ceramic rings to the filter (Don't wash or change these once you place them inside).

For your question on the bacteria, i agree with admael. The tanks are overstocked. When there is not enough nitrites/ammonia, some of the bacteria do die off (something like starvation). When there's more, they increase in numbers.

[pingapple]

Thanks for you opinions. My tank had the problem of high nitrate once. It was fixed after replacing most of the filter media gradually. This started my questions about what should be the right cleaning and replacing schedue for mechanical filter media and bio-media. How much BB will be lost after washing throughout with tank water and treated tap water? And a lot other questons ...

Thinking twice, my idea should be wrong - "bateria can survive with one mouth of rice but it can eat 10 bowls of rice without problem"

If half the BB is taken away, it will take 1 to 2 weeks for them to multiply to the original amount. During this 1 to 2 weeks, the ammonia and nitrite concentration will be in average about 50% higher than the original very low concentration. So, it should be fine for my anglefish.

I would like to know how you guys can successfully keeping fishes. For me, it was not that easy. My only stable tank is a 5 gallon tank runs with UGF for 5 little serpae tetras. But I vacuum the gravel everyday.

I believe that the key to success is not about equipment but correct maintenance schedule and right kind and right amount of fishes put together.

[stormhawk]

You are only required to change the top half of the media if necessary, and washing it under your tank water, or replace with fresh media. You are right on the key to success, but the use of proper equipment also plays a role. The simple fact is to maintain an ecological balance in the tank. I don't think you'd overfeed your angel, so replacing the top part of the filter media is fine.

[TOFU]

I think you only need to change your mechanical filter. And if im not wrong, lfs change their water everyday, that is why they can overstock