Does bacterial growth actually reduce GACs ability to work?

[rennjidk]

I keep seeing this posted over and over again with much debate. If I add 6 months worth of carbon to a media reactor, does it actually last for 6 months, or will it all be rendered useless after a few weeks due to bacterial growth clogging the pores?

 

[DanyL]

I don’t think I’ve seen activated carbon deflation rate linked to bacterial growth before.

I mean, does get clogged after a while, but it’s not just bacteria that grows there, but all kind of other stuff with larger particle size, as well as larger organisms and just plain dirt.

The other side of this is that a large amount of activated carbon can indeed deplane faster, because outside the toxics that it would remove, it’ll also bound to other useful trace elements from the system and will keep doing so until it’s depleted.

That means that of the ratio of toxics to trace elements is low (and it is), once the toxics are ran out it’ll mostly bound just traces.

I guess given both of these points, it doesn’t make much sense to keep 6 month worth of carbon in tank, but to split it to about a month’s worth portions and replace it when the water turn slightly yellow, which is the current consensus in the hobby.

 

[Dan_P]

I keep seeing this posted over and over again with much debate. If I add 6 months worth of carbon to a media reactor, does it actually last for 6 months, or will it all be rendered useless after a few weeks due to bacterial growth clogging the pores?

GAC can probably do it’s job for many months and it is actually the bacteria growth that could be making this possible in aquarium use. The bacteria growing on the carbon seem to be consuming the concentrated organic matter GAC removes from the water. The older GAC bed is probably better referred to as a biofilm reactor on GAC.

I typically change GAC every three months because I see a slow down in water flow. Bacteria and sometimes sponge growth partially clog the GAC bed. At one point I thought what the hobby narrative said about frequent GAC changes was true and removed my three month old GAC reactor thinking that it was not working and therefore wasn’t needed to keep the water colorless. I was surprised when the aquarium water became noticeably colored within two weeks. I cannot comment on how well an old GAC bed removes coral toxins or medications.

So, for my 100 gallon system, I use ~1 liter of Marineland GAC (the cheap stuff according to hobby wisdom) in a reactor and change it when the flow slows , usually by 3-4 months.

 

[rennjidk]

So, for my 100 gallon system, I use ~1 liter of Marineland GAC (the cheap stuff according to hobby wisdom) in a reactor and change it when the flow slows , usually by 3-4 months.

Have you noticed any reduction in trace elements doing it this way?

 

[Dan_P]

Have you noticed any reduction in trace elements doing it this way?

I don’t test but dose iron and CheatGro weekly. This is enough to keep the macro algae healthy and growing quickly.

 

[Randy Holmes-Farley Verified Community Expert]

I do believe that bacteria coating GAC will limit the ability of dissolved organics to bind under the bacteria. I also don’t think there is much one can or should do to prevent it.