Passive Diffusion in HOB Filter
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Old 02-09-2015, 05:40 AM   #1
Rinful
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Passive Diffusion in HOB Filter


So I was looking at my shiny new hob filter (aqua clear) for my 4 gallon when the thought hit me. Looking at numerous, what I assume to be co2 bubbles loitering around the chamber of the filter; sponges, media, etc… When my regulator turns off those same co2 bubbles would still be passively diffusing into the tank. What if… bear with me here… someone was to put filter media or sponge halfway down/up the chamber to leave open space on the bottom to inject a large bubble of co2 trapped there. The media would keep the bubble from escaping and would diffuse inside the filter for it to be distributed more efficiently around the tank; essentially making the hob filter one giant passive diffuser, instead of traditionally a bulky diffuser inside the tank. I can see one limitation for this already in that the biological filtering of the HOB itself will be limited, but in an already cycled/mature tank, a lot if not most of the bacteria would be in the substrate.
Will probably do an experiment on this in the future when I have the time but just throwing the idea out there for now.
Any input, suggestions? What do you guys think about it?
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Old 02-09-2015, 05:49 AM   #2
burr740
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You dont even need to raise the sponge up. AQs make excellent diffusers due to how the water passes through the media. (unlike cartridge type HOBs) I use an AQ20 on a 20gal @ 2-3 bubbles per second. Im sure larger models could handle more. I put a piece of cotton ball or chopstick in the co2 line to pre-diffuse the co2. This give the propeller a bunch of tiny bubbles to work against, instead of one big one. Then run the line directly into the intake. 100% dissolution.





Here is a recent in-depth discussion about it, page 4 specifically - http://www.plantedtank.net/forums/sh...d.php?t=810874
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Old 02-09-2015, 06:04 AM   #3
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I'm doing the same thing too, I got a GLA diffuser running under the aqua clear too, works like a charm (plants pearling in low/med light). Just putting the idea out there as before I switched to paintball I was using the fluval 20 g, so I wanted to see if the method I just described could diffuse co2 better than the regular bulky acrylic diffuser it comes with.
Really just curiosity lol.
Thanks for the link, skimmed through it before writing this thread will go back and read it some more.
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Old 02-09-2015, 06:13 AM   #4
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Raising the sponge up to create a lower water column is an interesting idea. Not sure it would be any better though. At least in my case, it'd be hard to improve on 100% dissolution.
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Old 02-09-2015, 06:31 AM   #5
Rinful
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True that
I remember reading somewhere passive diffusion was 100 percent too just horrible at distribution, makes sense. Interesting too, did not know AQ went from bottom up. Going to be moving my Paintball setup to a new 10 gallon in the future so wanted to get some opinions on this theory, especially since my backup regulator got a drifting NV.
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Old 02-09-2015, 01:34 PM   #6
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I'll preface this comment by saying that I think tying the C02 line into the AQ intake is a good method for dissolving c02 in to the water column, in fact, I've switched to this method after reading a similar discussion on this forum. However, I disagree that it achieves 100% dissolution, for the following reasons.

1. If you look top down into the AQ filter directly over top of the motor (the chamber where the intake pipe enters) you'll see a small hole. I think that this is specifically there to allow gas bubble to escape while the motor is 'priming' when it first starts up. As a result some of the C02 bubbles can also escape from this hole before they reach the main filter chamber.

2. I have to imagine that some of the CO2 gas bubbles off in the waterfall return to the tank.
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