gravel as bio media

I'm not sure I understand the question. Gravel hosts the "good" bacteria but is not neccesarily a biofilter. I'm sure Wetman, RTR, Matak and Faramir will be to my rescue soon.
 
Rescue, I doubt it, but JMHO... Any large surface area material can serve as a biosubstrate. However, a sponge will serve far better, as it will be more resistant to clogging and be easier to clean.

I would not suggest small gravel unless you plan on rinsing daily.

HTH
 
Surface area

What you are interested in, primarily, is surface area.

Gravel is better than nothing, but not as good as sponge, or ceramic media that have internal pore spaces like sponge or lava type rock does. Some pond filters used gravel long ago, but lighter, easier to clean materials, with more usable pore spaces came along.

Then you also might have to be concerned about the weight that the filter can support -- you wouldn't want anything to crack.

Many of the bio media I've seen ads for also mentioned the ability of the media to self-clean, that is to shed dead bacteria so that the pore space is not totally clogged up.

More often when someone mentions adding gravel to a filter, they are trying to seed the filter with bacteria from the gravel in one tank to a new tank that has no bacteria at all, to jump start the cycle.
 
I am assuming that the large surface area is due to oxygen. So does the sponge serve as a better biofilter because of the flow of water and the greater concentration of oxygen in the water flow.
 
alright sweet. my mind is almost cleared now.

the reason why i asked was because im using a HOT magnum.
and i doesnt use sponge, instead it uses filter floss. the the last time i used filter floss, it became very densely pack, therefore, i wasnt sure if there was any surface area in between.
 
The surface area is for bacterial attachment - the nitrification bacteria cannot metabolize unless attached. The sponge is preferable because structurally it holds its open spaces better for water flow (which does bring in both oxygen and the dissolved nitrogenous waste). Gravel clogs much too easily. The proportions of open space to surface area are better in sponge or well designed bioballs.

Personally, I am one of the folks who is neurotic about self-cleaning biomedia. I want it to be able to shed old biofilms and regrow fresh ones without my intervention. I don't want any clogging of biomedia by old bacterial growth.
 
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