HOB Filter and CO2 Offgassing
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Old 09-12-2013, 12:05 AM   #1
SunDevil76
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HOB Filter and CO2 Offgassing


So I am going to be setting up a DIY CO2 system next week, and I want to maximize the CO2 levels in the tank (because DIY CO2 doesn't provide as much as pressurized so I'm told) but I recently found out that the surface agitation caused by the HOB filter will cause outgassing of CO2, making it hard to keep adequate levels.

Basically I am thinking of replacing the plastic bio-filtration tray that is positioned in the filter's out-take (?) area with a sponge designed as biomedia. Will this reduce surface agitation enough to prevent outgassing, while still providing the surface area for growing beneficial bacteria? Will the increase of plants providing O2 be able to make up for the reduced O2 levels caused by reduced surface agitation?

Thanks in advance,
Jack G

Last edited by SunDevil76; 09-23-2013 at 12:02 AM.. Reason: More specific title
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Old 09-12-2013, 06:07 PM   #2
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Anybody? I want to make this work without buying a new filter.
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Old 09-12-2013, 06:39 PM   #3
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Your idea might help a bit but I think you'd still have a good amount of surface agitation simply from the water coming out of the HOB onto the surface of the water on the tank -- unless you fill your water level higher so that the water doesn't have as much drop from the "out-take" onto the tank water.

How many of and/or how big are the bottles for your DIY CO2? I've seen someone go nuts with 5, half gallon bottles. I'd say he's pushing more than my pressurized at the moment!

As for O2 levels, are you concerned for fish? I don't want to say don't worry about your fish at DIY levels, but I can say that I actually turn my HOB off during my injection period (~8 hours) to maximize my co2. But then again, I have a Koralia agitating a section of the surface just to make sure some gas exchange is going on. I'm still evaluating this part because I'm trying to test how long my tank will last. Then there are pressurized guys who just inject and don't even use an aerator or anything at night. They either go low or turn off at night.

Just try it out. Maybe just add more bottles. That has the added advantage of keeping things a bit more stable as the instability will just invite algae. I used to do DIY but I was cheap so I let it run down before I made new batches. I had a fairly strong light too so you can imagine the glorious algae plantations.

Ultimately, you want to push enough co2 to keep the HOB running, because overall agitation with o2 and co2 exchange is good throughout the entire co2 period, its supposed to keep the co2 level stable. Good pressurized systems are the easiest to achieve this but I'd venture that theDrake and his 5 bottles must be coming close to it if it hasn't already done so.
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Old 09-12-2013, 07:10 PM   #4
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Quote:
Originally Posted by ipkiss View Post
Your idea might help a bit but I think you'd still have a good amount of surface agitation simply from the water coming out of the HOB onto the surface of the water on the tank -- unless you fill your water level higher so that the water doesn't have as much drop from the "out-take" onto the tank water.

How many of and/or how big are the bottles for your DIY CO2? I've seen someone go nuts with 5, half gallon bottles. I'd say he's pushing more than my pressurized at the moment!

As for O2 levels, are you concerned for fish? I don't want to say don't worry about your fish at DIY levels, but I can say that I actually turn my HOB off during my injection period (~8 hours) to maximize my co2. But then again, I have a Koralia agitating a section of the surface just to make sure some gas exchange is going on. I'm still evaluating this part because I'm trying to test how long my tank will last. Then there are pressurized guys who just inject and don't even use an aerator or anything at night. They either go low or turn off at night.

Just try it out. Maybe just add more bottles. That has the added advantage of keeping things a bit more stable as the instability will just invite algae. I used to do DIY but I was cheap so I let it run down before I made new batches. I had a fairly strong light too so you can imagine the glorious algae plantations.

Ultimately, you want to push enough co2 to keep the HOB running, because overall agitation with o2 and co2 exchange is good throughout the entire co2 period, its supposed to keep the co2 level stable. Good pressurized systems are the easiest to achieve this but I'd venture that theDrake and his 5 bottles must be coming close to it if it hasn't already done so.
Yeah i'm worried about some of the O2 levels for the fish, but I would like consistent levels to avoid algae like you said. I only have one two liter bottle at the moment but I can always add another. Would it be best to keep them on alternating schedules (filling one and waiting a week or so to do the other one) so that they don't all run out at once?
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Old 09-12-2013, 07:16 PM   #5
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I have the quietflow 50 and I rigged it up with a diy baffle. I took a water bottle cut the ends off and cut down the middle. It redirects the water flow to the sides greatly reducing surface agitation. Google hob filter baffle. I did this because I picked up a dwarf gouramio and a small angelfish. Read that they like low flow. Im sure it helps reduce the gassing of the co2 as well.
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Old 09-12-2013, 07:26 PM   #6
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Quote:
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I have the quietflow 50 and I rigged it up with a diy baffle. I took a water bottle cut the ends off and cut down the middle. It redirects the water flow to the sides greatly reducing surface agitation. Google hob filter baffle. I did this because I picked up a dwarf gouramio and a small angelfish. Read that they like low flow. Im sure it helps reduce the gassing of the co2 as well.
Cool i'll look into that. I'll probably just end up doing a combination of all these methods we discussed. I'll try putting the sponge in the outflow of my filter, i'll keep water levels higher, if the sponge hasn't cut back on surface agitation i'll add a baffle, and maybe two 2l bottles as reactors. Thanks!
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Old 09-16-2013, 12:17 AM   #7
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The more I keep looking into this topic the more I keep second guessing myself. I even looked into canister filters but they are way too expensive. I need some more opinions on how to significantly reduce CO2 offgassing with my current filter without reducing filtration capacity.
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Old 09-16-2013, 12:54 AM   #8
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Just keep your water filled so that there is no drop off. You'll have a little degassing I would imagine but it'll be ok. I use an hob on my 10 with pressurized co2. I don't run my co2 that high and I get great growth. Fear not!
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Old 09-16-2013, 08:31 AM   #9
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Just keep your water filled so that there is no drop off. You'll have a little degassing I would imagine but it'll be ok. I use an hob on my 10 with pressurized co2. I don't run my co2 that high and I get great growth. Fear not!
Cool good to know. Do you use a baffle for your hob?
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Old 09-22-2013, 11:12 PM   #10
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So I tried making a sponge type baffle that seems pretty ineffective. When I do keep the tank filled up high it does reduce a lot of the surface agitation and the splashing. However, inside the filter itself is a waterfall type effect. It is more of a trickle with noise when I leave the bio-filter tray in, but it is a smooth quiet waterfall when I remove it. Will this prevent me from keeping good levels of CO2 in my tank? Should I instead invest in a sponge filter? Safe to say canister filters are out of the question due to their cost and it would be overkill for my 25 gal.
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Old 09-23-2013, 09:50 PM   #11
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My advice would just be to keep things as is and add DIY co2. I know when I first started, I was so impressed with the growth that it made me get a pressurized system ASAP. I had 2 HOB on a 29 gallon, 2 bottle setup. So you will get great results without doing much, at least I did.

For all practical purposes though, I have to run about 1/3 more CO2 if I want my drop checker to read the same when I have added a HOB to my tank while keeping the water level high. So, you are loosing about 1/3 or so, in my experience. It's really no big deal though, if your tank is doing well, any added co2 will be very welcomed and you will see good results.

Just saying, I wouldn't think to much about it.
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Old 09-23-2013, 10:30 PM   #12
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You don't want to have NO surface agitation either, because it makes it much harder to hit that line where you have enough CO2 without it being too much. Especially overnight when plants and fish give off CO2 - you won't be able to shut it off at night remember.

I say run with what you have, monitor the levels, add more bottles if necessary, but give a full 72 hours to build the concentration up before you add more.

How do you plan on diffusing the CO2 in the water?

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Old 09-23-2013, 11:10 PM   #13
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Quote:
Originally Posted by Whiskey View Post
You don't want to have NO surface agitation either, because it makes it much harder to hit that line where you have enough CO2 without it being too much. Especially overnight when plants and fish give off CO2 - you won't be able to shut it off at night remember.

I say run with what you have, monitor the levels, add more bottles if necessary, but give a full 72 hours to build the concentration up before you add more.

How do you plan on diffusing the CO2 in the water?

Whiskey
I just bought some cheap regular airstones for now, just because they were like 2 bucks. I know these are terrible for diffusing CO2 but until I get a proper diffuser they should be fine in the short term, right? I am thinking about using a wooden airstone or a Hagen ladder for the long run.
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