Co2 reactor questions - The Planted Tank Forum
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post #1 of 13 (permalink) Old 01-16-2020, 01:26 AM Thread Starter
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Co2 reactor questions

Hello.

So after realizing that my Co2 levels were low due to not enough Co2 being put into the water through my neo diffuser + AC20.
I've been revisiting my reactors including one I built today which is a rex grigg style one.

The thing that I'm having trouble with is air bubbles that are being introduced into both reactors from my pump which is an EcoPlus 396.

The basic design similarity between the two is I've got 3/4" schedule 40 PVC running from the pump into each reactor with a schedule 40 ball valve on the output side.

Now to the issue, with my cerges reactor I have a 10" water filter housing and when I have the valve full open the water level drops to almost half way with the rest being air and as I close the valve it fills back up with water again only being about 90% full of water with the valve fully closed.

With the griggs style reactor I have no idea what the water levels are, but with the valve full open I have tons of bubbles coming through the output with only big air bubbles coming out instead of micro bubbles when I have the valve about 75% closed.

In both cases it's just air, not Co2 or anything as I've not hooked that up.

My questions are:
What is causing this air being introduced into the system, is the 3/4" PVC too large for my pump?
Would it be better to replace the hard line PVC with tubing? Or would lowering the size of the PVC pipe to 1/2" work also.
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post #2 of 13 (permalink) Old 01-16-2020, 01:46 AM
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Originally Posted by Quesenek View Post
Hello.

So after realizing that my Co2 levels were low due to not enough Co2 being put into the water through my neo diffuser + AC20.
I've been revisiting my reactors including one I built today which is a rex grigg style one.

The thing that I'm having trouble with is air bubbles that are being introduced into both reactors from my pump which is an EcoPlus 396.

The basic design similarity between the two is I've got 3/4" schedule 40 PVC running from the pump into each reactor with a schedule 40 ball valve on the output side.

Now to the issue, with my cerges reactor I have a 10" water filter housing and when I have the valve full open the water level drops to almost half way with the rest being air and as I close the valve it fills back up with water again only being about 90% full of water with the valve fully closed.

With the griggs style reactor I have no idea what the water levels are, but with the valve full open I have tons of bubbles coming through the output with only big air bubbles coming out instead of micro bubbles when I have the valve about 75% closed.

In both cases it's just air, not Co2 or anything as I've not hooked that up.

My questions are:
What is causing this air being introduced into the system, is the 3/4" PVC too large for my pump?
Would it be better to replace the hard line PVC with tubing? Or would lowering the size of the PVC pipe to 1/2" work also.
I just built a rex griggs reactor. Mine has a clear pvc tube as the main component so I can see what is happening inside. I had the same issue with a lot of air being in the tube (its noisy, you can hear it when this is the case). To solve this problem (while the filter is running) you need to turn the rex griggs reactor upside down. This will force all the air to go out the return side of the reactor. Keep it upside down till air bubbles stop coming out (about 30 seconds or so), then return it to its normal orientation. From that point onward it should run fine.


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post #3 of 13 (permalink) Old 01-16-2020, 02:22 AM Thread Starter
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Originally Posted by minorhero View Post
I just built a rex griggs reactor. Mine has a clear pvc tube as the main component so I can see what is happening inside. I had the same issue with a lot of air being in the tube (its noisy, you can hear it when this is the case). To solve this problem (while the filter is running) you need to turn the rex griggs reactor upside down. This will force all the air to go out the return side of the reactor. Keep it upside down till air bubbles stop coming out (about 30 seconds or so), then return it to its normal orientation. From that point onward it should run fine.
Thanks for the reply.
So it looks like going hard line PVC was a bad idea because I can't flip it.

Do you have yours running after your canister filter? If so do you have to use a valve to build up more pressure inside of the reactor?
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post #4 of 13 (permalink) Old 01-16-2020, 02:57 AM
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Originally Posted by Quesenek View Post
Thanks for the reply.
So it looks like going hard line PVC was a bad idea because I can't flip it.

Do you have yours running after your canister filter? If so do you have to use a valve to build up more pressure inside of the reactor?
Here is a picture of my setup:



The canister filter return line goes directly into the top of the reactor. The bottom of the reactor has another line that goes directly into the aquarium. There is no ball valve anywhere in the process. My canister filter is frankly not powerful enough to want any kind of flow restriction or bypass.

I played around with trying to get it to fill without turning it upside down by putting my finger over the return spout in the aquarium (cutting the flow). This did nothing unless I also had an extended air hose attached directly to my co2 airline tube intake (no check valve inbetween) then the water level rose to the level of the air hose. At that point it would go slightly higher then the air hose but water started coming through the line even though I extended the air hose above the level of the aquarium (water pressure was too high for it to be otherwise) - does that make sense?

Anyway bottom line is that for all intents and purposes I was unable to get the water level to rise significantly above the point where the airline tube entered the reactor.

If left running for a period of days the air "should" (in theory) leave the reactor and it should fill entirely with water. This will be due to the air dissolving very slowly into the water. But this will take a while, at least a few days, maybe a week or more depending on how much water is involved. This is just me theorizing, I haven't tried it.

Honestly if it were my setup... I would rip out the hardline pvc connections and redo them with barbed fittings and flexible tubing. Even if you get this problem solved, sooner or later you will have an issue that will require you to drain the tank etc and then your reactor is down for the count till you resolve the problem a second time. Better to deal with this problem now when all your plants won't be dead/covered in algae by a week long delay in getting co2 back up.
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post #5 of 13 (permalink) Old 01-16-2020, 03:19 AM Thread Starter
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Originally Posted by minorhero View Post
Here is a picture of my setup:



The canister filter return line goes directly into the top of the reactor. The bottom of the reactor has another line that goes directly into the aquarium. There is no ball valve anywhere in the process. My canister filter is frankly not powerful enough to want any kind of flow restriction or bypass.

I played around with trying to get it to fill without turning it upside down by putting my finger over the return spout in the aquarium (cutting the flow). This did nothing unless I also had an extended air hose attached directly to my co2 airline tube intake (no check valve inbetween) then the water level rose to the level of the air hose. At that point it would go slightly higher then the air hose but water started coming through the line even though I extended the air hose above the level of the aquarium (water pressure was too high for it to be otherwise) - does that make sense?

Anyway bottom line is that for all intents and purposes I was unable to get the water level to rise significantly above the point where the airline tube entered the reactor.

If left running for a period of days the air "should" (in theory) leave the reactor and it should fill entirely with water. This will be due to the air dissolving very slowly into the water. But this will take a while, at least a few days, maybe a week or more depending on how much water is involved. This is just me theorizing, I haven't tried it.

Honestly if it were my setup... I would rip out the hardline pvc connections and redo them with barbed fittings and flexible tubing. Even if you get this problem solved, sooner or later you will have an issue that will require you to drain the tank etc and then your reactor is down for the count till you resolve the problem a second time. Better to deal with this problem now when all your plants won't be dead/covered in algae by a week long delay in getting co2 back up.
Thanks for the detailed post definitely will come in handy when I get everything together.

When I can I'm going to be changing out my tidal 110 for a canister filter because I can run an inline reactor without other things in the tank.
I could get everything running with what I have + soft tube, but I have my doubts about getting a stable Co2 level with my HOB setup on my 55 gallon.
This is my first large tank that I've actually tried to get everything working stable high tech without a canister filter so it's been a learning experience of what works and what doesn't.
So far I've got my drop checker changing to green, but I've already seen it switch between green and blue today with my current setup so things aren't stable with a diffuser + HOB setup.

Also another question, are the PVC fittings you do have are they 3/4"?

EDIT 1:
I did a little more messing around with the cerges reactor. That air bubble that forms is solved by turning the reactor upside down until it blows out and it wasn't caused by my pump/fittings as I previously thought. I realize now if I had an air purge button that it wouldn't be an issue.

EDIT 2:
I solved my rex grigg reactor issue.
Everything is still the same as before with the hard line PVC however I've found a way that I can purge the reactor of air is to hook up the pump to the output for a few minutes until I see no bubbles and then keeping everything under water I can hook it up to the input and everything works as expected no air bubble left in the chamber. Turning the pump off only puts a slight bit of air in the system that blows out in about 30 seconds to a minute. I will have to test this on my actual tank, however in my test tank everything seems to be working as expected.

Last edited by Quesenek; 01-16-2020 at 06:45 AM. Reason: Edited for how I solved my issues.
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post #6 of 13 (permalink) Old 01-16-2020, 11:46 AM
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Originally Posted by Quesenek View Post

Also another question, are the PVC fittings you do have are they 3/4"?


EDIT 2:
I solved my rex grigg reactor issue.
Everything is still the same as before with the hard line PVC however I've found a way that I can purge the reactor of air is to hook up the pump to the output for a few minutes until I see no bubbles and then keeping everything under water I can hook it up to the input and everything works as expected no air bubble left in the chamber. Turning the pump off only puts a slight bit of air in the system that blows out in about 30 seconds to a minute. I will have to test this on my actual tank, however in my test tank everything seems to be working as expected.
Glad to hear you solved it!

For what it is worth the barbed fitting at the end that attach to my flexible tubing are 3/4" but I left room for everything to be changed over to 1" fittings down the road when I move this reactor to a 120 gallon tank. The clear tube that make up the main part of the reactor is 2"
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post #7 of 13 (permalink) Old 01-16-2020, 01:30 PM
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I just built a rex griggs reactor. Mine has a clear pvc tube as the main component so I can see what is happening inside.
I had considered doing this when I built mine, but was concerned about potential algae and slime build-up that would eventually make viewing impossible. If you remember, I'd appreciate it if you would update this thread in 3-4 months to let us know if this takes place.
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post #8 of 13 (permalink) Old 01-16-2020, 03:18 PM
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I had considered doing this when I built mine, but was concerned about potential algae and slime build-up that would eventually make viewing impossible. If you remember, I'd appreciate it if you would update this thread in 3-4 months to let us know if this takes place.
I probably won't remember in this thread, but I definitely will remember in my tank journal. It is definitely a concern of mine. My thought is that since the reactor is not in direct light the regular buildup of algae/slime will not get thick enough that I won't be able to see what is going on generally. Certainly its not so bad with the translucent tubes for my canister filter and they are already 8 months old at this point.

Anyway the tank in question is in my signature as the Quarantine to High Tech.
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post #9 of 13 (permalink) Old 01-16-2020, 04:53 PM
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I run Grigg's on all my tanks and do not vary the design much at all unless I get down into the 10-20 gallon size. I run one on 125 gallon at the same size as 75 gallon with no changes. One of the most common things that I see on building the Grigg's is that folks want to improve the design but overshoot on bad theories!
My first question on design changes? Do I know enough more about fluid flow to go beyond a design that works so well it has become almost a "standard"? In my case, the answer is a definite "NO" and I do not try to reinvent something that works so well!
One of the ideas that do not fit in my thinking is that one can control the pressure in the reactor enough to change how much CO2 is absorbed into the water. I keep in mind that it is very hard to increase pressure on an item that is nearly open at both ends! On a canister filter, we are only looking at very small pressure (less than 3 PSI?) and getting enough pressure to change the absorption has to go lots higher than that, in my view.
I do find it works much better for me when I leave the reactor loose to be able to swing it up to let air pass out of the body. I find I can't get a good restart/prime if there is air or water left in the body which happens every filter cleaning. Air will always go up to pass through water but not if it has to go down first. It just sets there as an airblock to water flow starting again and I often will only get a trickle until I tilt the reactor bottom to top.
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post #10 of 13 (permalink) Old 01-16-2020, 05:17 PM
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I had considered doing this when I built mine, but was concerned about potential algae and slime build-up that would eventually make viewing impossible. If you remember, I'd appreciate it if you would update this thread in 3-4 months to let us know if this takes place.
You could probably make some sort of removable cover to block out light, maybe a sock or a piece of pipe insulation.
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post #11 of 13 (permalink) Old 01-16-2020, 05:30 PM Thread Starter
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Originally Posted by PlantedRich View Post
I run Grigg's on all my tanks and do not vary the design much at all unless I get down into the 10-20 gallon size. I run one on 125 gallon at the same size as 75 gallon with no changes. One of the most common things that I see on building the Grigg's is that folks want to improve the design but overshoot on bad theories!
My first question on design changes? Do I know enough more about fluid flow to go beyond a design that works so well it has become almost a "standard"? In my case, the answer is a definite "NO" and I do not try to reinvent something that works so well!
One of the ideas that do not fit in my thinking is that one can control the pressure in the reactor enough to change how much CO2 is absorbed into the water. I keep in mind that it is very hard to increase pressure on an item that is nearly open at both ends! On a canister filter, we are only looking at very small pressure (less than 3 PSI?) and getting enough pressure to change the absorption has to go lots higher than that, in my view.
I do find it works much better for me when I leave the reactor loose to be able to swing it up to let air pass out of the body. I find I can't get a good restart/prime if there is air or water left in the body which happens every filter cleaning. Air will always go up to pass through water but not if it has to go down first. It just sets there as an airblock to water flow starting again and I often will only get a trickle until I tilt the reactor bottom to top.
Thanks for the reply, when I can I will be replacing the hard line PVC for hose barbs for use with a canister filter so I can invert it to purge the air pocket.
For the valve on the output side, I just added it because the pump is much too powerful for my setup and I would probably need a 5ft rex grigg reactor or larger for it to be slowed down enough for my tank. I doubt I will need it after I acquire a canister filter and it has all of the media slowing the flow down from the filter. For this situation it was a case of using what I had, not really purpose bought materials like the pump. FWIW the reason why I brought up the pressure thing is because I saw people saying that's what you need to do with a reactor to get the Co2 bubbles to be diffused into the water, I realize now that with the rex grigg style reactor the height of the reactor needs to be changed to accommodate the tank.

Aside from that it's just a plain rex grigg reactor, no changes to the actual design.
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post #12 of 13 (permalink) Old 01-16-2020, 08:26 PM
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Yes, it is easy to find differing views of how things may work and why. No argument but I just do not agree as my reactors do not give me any visible bubbles and I have no added items to increase pressure. Sometimes the output is a spray bar, sometimes just and open PVC fitting, depending on what water movement I want at the time. I do run canisters on all tanks with CO2, even the ten gallon. That one was the most trouble to stop bubbles passing through as I thought it had such small filter ( Zoomed 501) that it had to have a small reactor and I way undersized by going to 3/4 inch pipe! I now feel it is necessary to have enough width for the CO2 to meet the water, swirl around long enough to be absorbed and enough length for it not to reach the exit before it gets small enough. I feel time of contact to be the more important item than pressure as there is very little pressure built up when the output is simply an open pipe.
So to make my day as simple as possible, I now use almost all the same size for all tanks. Only time I would change is when I have space problems like for the ten setting on a shelf with the small canister alongside it.
I find no problem at all with letting the bubbles chase around far longer if they are in a way oversized reactor, so I go with 1 1/2 inch 18" long and let the small filters just work the same as the larger tanks and filters. The difference for me is that the big reactor required pulling the shelf out from the wall and letting the reactor hang down behind it! Lots a bit odd to have an 18-20 inch reactor tied to a 12 inch tank but it works so fits for me. The bubbles can stay in the reactor all week as long as they are not exposed to the air to gas off.
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post #13 of 13 (permalink) Old 01-16-2020, 08:48 PM
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One of the most common things that I see on building the Grigg's is that folks want to improve the design but overshoot on bad theories!
I know we’ve discussed this before and I still feel that, if we don’t try to improve things, we can’t make them better. I did modify my Griggs, mainly because I couldn’t take the gurgling from the CO2 build-up anymore. While my Griggs length and diameter, given my CO2 needs and tank size, are going to differ from others, I did solve my problem. The modification I made is here: https://www.plantedtank.net/forums/9...l#post11087063

However, I found that the ‘silencer’ tube is all that was needed. The “2” CO2 tube segment” connected to the CO2 input tube was not needed.

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I now feel it is necessary to have enough width for the CO2 to meet the water, swirl around long enough to be absorbed and enough length for it not to reach the exit before it gets small enough. I feel time of contact to be the more important item than pressure as there is very little pressure built up when the output is simply an open pipe.
I came to the same conclusion: that the key is the contact time with the swirling bubbles. Where the CO2 forms a growing layer at the top, there is not enough CO2-water surface interface to dissolve the CO2 as efficiently as the bubbles do. Thus, pulling this CO2 gap through the silencer, converting it into bubbles again, reduces that gap.
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