# Any reason to not put CO2 diffuser in HOB filter?



## Higher Thinking (Mar 16, 2011)

Off-gassing is definitely your biggest concern. Because of agitation that occurs within your (open topped) filter and then the entrance into the tank, the water will off-gas the CO2 more rapidly. Depending on how effective the diffusion is and how much agitation occurs with the water entering the tank, you may or may not find it an effective method. Sorry for the ambiguous answer, but there are several variables which only you will be able to assess.


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## Aurie (Jun 3, 2013)

I set up co2 (diy) in my 5.5 gallon defusing through a chop stick. Worked so well that if I didn't have a betta in that tank my fish would have been gassed the first night. I put it in my aqua clear via the little hole and run an air stone at night and now it seems to have equalized itself. I don't have any pearling either way, but this way it makes me feel better and BOTH ways have my plants growing like weeds. My s. repens is getting huge (time for its first cut) and the star grass I got is sending out new growth and is very green. The old parts are the same, but not dying. I can easily replace the old parts now and I just got the stuff 2 weeks ago. I dose 4-10 drops of aquariumfertilizer micro/macro mix but soon I'll move onto individual nurtients once this mixed batch is used up.

There are pros and cons. If you keep the water level up and the water doesn't tumble down into it you'll have less off-gassing. I see little bubbles coming out of my filter and they go down towards the bottom. Dunno if they're co2 or o2 though.


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## pwu_1 (Oct 28, 2013)

What about the possibility of killing off the beneficial bacteria in the biomax media? The bacteria needs oxygen right? Would I possibly kill off some of the beneficial bacteria?


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## Edub (Mar 23, 2011)

pwu_1 said:


> What about the possibility of killing off the beneficial bacteria in the biomax media? The bacteria needs oxygen right? Would I possibly kill off some of the beneficial bacteria?


 
I doubt it, certainly not enough to cause your tank to re-cycle or anything. Theres a lot of surface agitation in your filter so that should provide plenty of oxygen. 

Honestly I think the only concerns you should have are off-gassing of co2 and if your diffuser stays clean and clog-free. I dont have much experience with aquaclear filters but if you put the diffuser "after" the media so it is only exposed to clean, filtered water you shouldnt have too much buildup on it. If, however, it is exposed to dirty water you'll probably have to clean it off from time to time.


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## talontsiawd (Oct 19, 2008)

I had some problems running it through the purge hole on one of my tanks. Mostly it was just hard to prime. However, I did have one incident where the filter media lifted and started spilling out the HOB housing. I believe it was a combination of air in the sponges, lack of maintenance causing a clog, and having that hole clogged not allowing enough by pass. With a clean filter, I would not expect it to happen. However, you will not run into that if you put the diffuser in the actual media basket anyway. Just saying, if you do go through the hole, which was very popular a few years ago, maintain your filter.


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## exv152 (Jun 8, 2009)

I would opt for a whole different filter if I was going to inject co2, let alone inject co2 inside the HOB. I've found HOBs to be pretty bad for off gassing, not sure why, probably because of the splashing of water on the outlet. But I always aim to introduce co2 as low as possible in the tank to give the co2 the best dwell time in water (in a good flow area), when using a disc diffuser.


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## talontsiawd (Oct 19, 2008)

exv152 said:


> I would opt for a whole different filter if I was going to inject co2, let alone inject co2 inside the HOB. I've found HOBs to be pretty bad for off gassing, not sure why, probably because of the splashing of water on the outlet. But I always aim to introduce co2 as low as possible in the tank to give the co2 the best dwell time in water (in a good flow area), when using a disc diffuser.


I found that use about 1.5x more CO2. That is quite a bit but it works just as well. I feel that a HOB adds some safety too by oxygenating the water more. The big downside to me is not the off gassing, it's keeping the water level consistent. 

The reason I don't use HOB's has little to do with CO2. If they were silent like my canisters and more attractive, I would actually consider switching over.


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## xmas_one (Feb 5, 2010)

Just put it in the tank on the back under the HOB so the bubbles will get blown around in the current.


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## pwu_1 (Oct 28, 2013)

Thanks for all the input. I think I ordered everything I need for my CO2 system. After thinking about it some more I decided to just put the diffuser in the tank. I'll be experimenting with placement to find a spot that will allow the bubbles to circulate well in the tank. Picked up an aquatek diffuser/bubble counter/check valve combo to diffuse the CO2.

Found a cheap 5lb CO2 tank off craigslist so going to pick it up later today and get it filled. The rest of the parts should arrive by end of this week so hopefully I'll get everything up and running this weekend.

Oh and the aquaclear HOB filter is really quiet. My 10 gallon tank is sitting on my office desk right in front of me. I work from home most days so I'm sitting at my desk 8-12 hours and I can just barely hear a low hum. Definitely not loud enough to bother me.


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## DarkCobra (Jun 22, 2004)

I've heard it suggested that exposure to light may accelerate clogging of the diffuser. Which could be avoided by placing the Atomic diffuser in the HOB. Can't say from experience, as I've only used the inline Atomic with a canister.

If I'm using an Aquaclear, I really have no need for a diffuser. Instead, I stuff a non-biodegradable cigarette filter (with paper removed) in the end of standard size flexible silicone CO2 tubing, then cut the end of the line and filter at a 45° angle. This breaks the CO2 into small bubbles. At first some bubbles may pass through the filter, but it soon clogs. Thereafter it's essentially a seal, but because both tubing and filter are flexible, when back pressure reaches a reasonable amount it will leak in a surprisingly controlled fashion; still producing a steady stream of small bubbles.

This I attach to the outside of the unmodified intake tube with zip ties, positioning the end so the bubbles will be drawn into the Aquaclear. The impeller breaks the bubbles down further, and since they were small to start with, you can't hear anything unless you listen very closely.

Finally, I raise the sponge in the media basket instead of putting it at the absolute bottom as usual. This helps remaining bubbles get trapped underneath and dissolve into the flow reactor-style, rather than escaping through the priming hole. I do not plug this hole unless it actually appears necessary. It usually isn't with the sponge properly placed, but if so another cigarette filter does the trick.

It's highly efficient. Beats other methods I've compared against. Though I haven't tried everything, I suspect it's sufficiently close enough to 100% that I stopped looking for superior methods; so long as I'm using a HOB.

I do notice the sponge doesn't gunk up as fast, particularly on the smaller filters like the Aquaclear 20. That may be evidence of decreased biofilter activity. It's not so noticeable on the Aquaclear 70. In all cases I have never seen ammonia or adverse effects on the tank. The plants probably make up any difference.


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