Should You Use the Activated Carbon Bag in Your Fluval Spec Aquarium?

The stock filtration system of a Fluval Spec series aquarium comes with three components of filter media.  They are:

  • Mechanical Sponge Filter – this is the foam filter block that fills most of the filter section.  In it are two holes that house the other two filter media that come with a Fluval Spec (or EVO) Aquarium.

fluval spec foam filter block sponge

  • Biological Filter – This is a bag filled with ceramic rings.  They are porous and have lots of surface area.  The function of all this surface area is to provide a place for the beneficial bacteria to grow.

fluval spec biomax box

  • Chemical Filter – This is a bag filled with activated carbon. Activated carbon has lots of surface area like the ceramic rings.  In addition, it has the ability to remove some dissolved orgaincs and toxins.

fluval spec sponge filter with carbon and biomax

Advantages of Using Activated Carbon in an Aquarium:

Some of the organics and toxins that activated carbon is claimed to remove include: bleach, chlorine, odors, and pesticides.  Activated carbon has special use in removing medications.  Once you are done with a dosing regimen to rid your fish of disease, carbon usage can be helpful to remove the remaining chemicals and get your aquarium back to a steady state.  If you choose to not use the carbon bag in your spec, make sure to keep it stored for such a time.

Disadvantages to Using Activated Carbon:

A few notable things that it won’t remove include nitrite and nitrate, two byproducts of a new aquarium that is not yet stocked with beneficial bacteria. So while it will help your water quality a bit, it will not work wonders and alleviate the root problems of an uncycled aquarium. Some people use activated carbon to keep odors at bay.  This goes back to a root cause problem.  Our aquarium, in it’s admiditally young life (10 months) has never smelled bad.  This is probably in the Too Much Information category, but i have taken the nasty water that I clean out the sponge filter, which is fully saturated in brown detris, and smelled it.  It actually is quite inert and has very little smell.  (I had my wife test this as well to verify it wasn’t just that I have no sense of smell.)

The big disadvantage that has kept me from considering ever using the activated carbon bag in our spec is that it removes trace elements.  We have setup this aquarium as a low light planted tank from the start.  Part of the care for a planted aquarium is to provide fertilizers to the water column.  There would be no use in placing activated carbon in a planted tank as it would remove the very trace elements that the plants are using.

Another big disadvantage to activated carbon media is the cost over time.  It can absorb material to the point where it can not absorb any more.  At that point, it needs to be replaced.  While the cost of replacement bags of carbon for the Spec line of aquariums is reasonable, it will add up over time.

Alternatives to the Activated Carbon Bag in the Spec Filteration System:

I think that having lots of surface area in the way of more biological media is much more beneficial than anything activated carbon can offer.  If you have a proper beneficial bacteria colony growing in your filtration system, that will probably take care of any issues you would run into with water quality. I would first suggest to all aquarist to not use the carbon bag and instead use two bags of Biomax.  This is what I started out with and it worked great.

Since then I have transitioned to using Seachem Purigen in our aquarium.  I use the stock foam filter block with a bag of Biomax in the top section and a 100ml bag of Purigen in the bottom section (folded over in half to fit).  That has been a very nice setup; the water is usually extremely clear. As I said earlier, I have never had odor problems and all the fish/shrimp/snails are healthy.

24 thoughts on “Should You Use the Activated Carbon Bag in Your Fluval Spec Aquarium?

  1. Hi, i just bought seachem purigen and i had a fishy smell coming through the bag and tank water. i was wondering if u had the same problem if so what did you do to get rid of it.
    Thank you, love your work!!

    1. The Seachem Purigen bag comes soaked in something to preserve it in storage – probably a variant of their water conditioner (Seachem Prime). If you have already put it in the tank that is fine. For next time, or now if it is still smelling, rinse it out in tap water very good, then put in a tupperware or other container with some water and dechlorinate the water. Then put it in the tank. Should take most of the offensive smell out.

  2. So it’d be best to flip The way fluval recommends setting up the tank? For the beneficial bacteria. Bio max on top, carbon on the bottom?

    1. Maybe. I’ve thought about this and I can’t be convinced that it matters much what order you put your filter media in (for this tank). I’m sure it will work fine either way.

  3. HI, I’ve been reading your posts about using Seachem Purigen to replace the carbon filter. As a fish newbie, I have a question: Is it not possible to get an exacto knife and cut out another section is the foam block to add the Seachem Purigen and ALSO leave in the carbon? Is that overkill? Would they work against each other in some way?

    Thank you for this blog!

    1. I don’t think there is enough material in the stock filter sponge to cut away and get another compartment. You can try.

      I don’t know that there is a problem with using activated carbon and purigen together, but I will restate my opinion in the article: There is no benefit to using activated carbon under normal circumstances for any aquarium. You just don’t need it.

  4. I have a Fluval Flex 125. The tank is planted. The filter has two foam compartments. I have removed the carbon bag & placed Purigen (two bags of 30g) in each side. I plan to replace Biomax gradually ovver time with Biohole Ultimate Mini filter media. Space is limited. As the bags of Purigen are small, could I safely add other media in to the same compartment & they both work? As long as water flows through, I can’t see why not. Thanks for a great article.

    1. It’s hard to visualize as I’m not intimately familiar with this model of Flex. It should work but know that water always takes the path of least resistance. If you pack media too tightly, water may tend to divert around to the portion of the sponge that surrounds the media.

  5. Hi. Do you think there is any benefit or problem with getting a second filter block, putting biomax in both compartments and putting it in the unused first section? Effectively doubling up on the filtration capacity?

    1. I don’t know what you mean by “unused first section”. What aquarium are you talking about?

  6. If I’m still in the process of cycling my tank would it be a good idea to switch out my charcoal with seachem purigen or wait till it’s cycled?

    1. I think you can do either (switch now or wait) and it shouldn’t affect your cycling effort too much.

    1. I’m not following what you mean by Seachem. Shoot a clarifying comment and I’ll follow up.

      The sponge can last virtually forever, provided you wash it out often (use methods I discuss here). You only need to replace the sponge if it tears (I’ve never had that happen) or if you let it get super dirty and you can’t get it unclogged (also never had this happen).

  7. I replaced the carbon filter that came with my Fluval Spec V Aquarium with a 100 ml bag of Purigen when I set it up a few months ago as per your advice. I am now wondering about the bag of Fluval Biomax. I can’t find any information regarding when or if it should be replaced. I rinse the Purigen and the Biomax in the tank water I have removed when I do my weekly water changes. Everything still looks very clean. I did read somewhere that the Biomax will collect toxins from the water and should be changed out periodically, but I have not been able to verify that. It seems like you would be getting rid of a substantial amount of your good bacteria if you change it out. Can you give me some info about this please?

    1. I don’t know of a situation where you would have to get rid of the bag of Biomax. Toxins? If you have toxins in the system, they will leach into the sponge filter, the substrate. . . everything. If you get ‘toxins’ in the tank not sure that getting rid of the biomax will solve the issue.

      I’ve used the same bag of Biomax for years at a time. I change them out occasionally but for no good reason (often just because I purchased a new tank and want to use the new media).

      Yes, when you replace any component of your filtration media, you are getting rid of some of your good bacteria. It’s not a big deal as there is plenty of remaining bacteria for filtration in the other media (sponge, purigen, etc.) not to mention all that is on plant leaves, substrate, etc.

Leave a Reply

Your email address will not be published. Required fields are marked *