DaveH's Inline RG reactor attempt

Tilting is definitely helpful for clearing air or excess CO2.

Your reactor is not set up like a stock Rex reactor which probably explains why it is working the way it is. Unless he has changed the design since I built mine the CO2 is supposed to enter through the side of the PVC tube a few inches below the top. That way the bubbles are immediately rising against the inflow. You have already diffused the CO2 and it is entering through the top as mist, the mist is flowing with the incoming water. I don't think you are going to get the same churning affect this way. The bubbles are so small when they enter that they don't have the same buoyancy as larger bubbles coming through the side would so instead of rising they are slowly getting pushed down. Almost working more like a delayed misting effect.

Are you monitoring the levels in the tank with a drop checker and getting the same response (response time too)?

captain_bu said:

Tilting is definitely helpful for clearing air or excess CO2.

Your reactor is not set up like a stock Rex reactor which probably explains why it is working the way it is. Unless he has changed the design since I built mine the CO2 is supposed to enter through the side of the PVC tube a few inches below the top. That way the bubbles are immediately rising against the inflow. You have already diffused the CO2 and it is entering through the top as mist, the mist is flowing with the incoming water. I don't think you are going to get the same churning affect this way. The bubbles are so small when they enter that they don't have the same buoyancy as larger bubbles coming through the side would so instead of rising they are slowly getting pushed down. Almost working more like a delayed misting effect.

Are you monitoring the levels in the tank with a drop checker and getting the same response (response time too)?

Click to expand...

That's actually an interesting perspective. My assumption was that the diffuser would produce smaller bubbles which would make it easier/faster to diffuse the bubbles. Perhaps the tiny bubbles are much less buoyant so they just drift along with the water rather than churning away at the top of the reactor.

But consider this: Say I introduce larger bubbles to the reactor using the regular way of drilling a hole in the reactor and putting the CO2 hose through it. Wouldn't those larger bubbles right from the CO2 float towards the top of the reactor, be munched up by the turbulence and turn into much tinier bubbles? Those tiny bubbles would simply go down the tube the same way that they do if they went through the diffuser. That would put me right where I am now. Hence my assumption that introducing bubbles that are already smaller would increase efficiency.

Well, perhaps my assumption is incorrect

Any physics experts care to opine? I am bent on having zero bubbles in the tank and if I have to uninstall the reactor and fool around with it a bit, that's no problem

Dave-H said:

The reactor has been silent and I got all the air out. Now it's just the diffuser and slightly less than 1 bubble/second. There are fewer bubbles than with the boyu but just barely. I can look into the clear pvc and see tiny bubbles swirling steadily down the tube. It does seem like larger bubbles go forcefully to the surface so maybe I will put a hose on the side as in the original designer.

In the pic you posted on that other thread your setup was essentially like mine (boyu/waterplant then rg reactor). Do you get bubbles? What is the filter gph and tank site?

Click to expand...

haha...so now you want my help?
:help: <-- thats you:hihi:

I run an eheim 2232 (106gph) (< 236 (159 gph)) thru a 20" length of 2" PVC
I dont get any bubbles (unless I turn my bubble rate up ridiculously high ~10bps and create the air pocket in the top and kill all of my fish) I only have 2 tanks...a 20gal long and a std 10gal...same filter/reactor setup on both

no bubbles and the water comes out with a "thick" look
doing the math, my reactor has a velocity of ~5.5 cm/s, yours would have ~8.25cm/s

now...that means that the size of the bubbles coming out would be different...but not amazingly so

using Stokes law for bubble kinematics to calculate the rise velocity (or in this case, solving for bubble radius since we know the velocity of the bubble we want)


Vst = 2gr^2/9v
or
r = sqrt(Vst*9v)/2g

in my reactor....Vst = 5.5 cm/s (or velocity at which the smallest bubble can still fight the flow velocity, or Vrise = 0cm/s, and thats only true for a straight line of flow from the reactor inlet to the outlet as the flow field slows as you get farther away from dead center) is .0157 cm or ~.16mm (a TENTH of a millimeter)

in your reactor where Vst = 8.25 cm/s...your bubble radius is .0192 cm or ~.19mm (~2 TENTHS of a mm)

heres a chart that "may" make it a litle easier to understand
1000 micrometers = 1 millimeter


I doubt your inline diffuser is putting out bubbles that small...sooooo...I think your reactor is working and "maybe" you didnt make it long enough (tho not likely from the looks of it) or your bubble rate is too high and needs to be tweaked (tho you said that its low...)

so...I dunno

**EDIT**
also...doubt youll be able to add that hose to the side now...basically youve cemented the whole thing together...

you might be able to drill a hole and force the tubing thru from the outside...but I dunno...never tried it (always did it before I cemented the top on)

my first design was just like RG (with side hole) except my HD and Lowes dont carry the 2x2x3/4 (threaded port) youd have to order it...so I jus went with a standard 2" Tee...I changed it to include the inline diffuser because I thought it was a better method to introduce the CO2

I havent seen any significant difference in the method tho, both produced "thick" water

Yea it's hard to get a clear story on why the reactor isn't working. So far we have the following concepts:

1) Some argue that once the air bubbles are cleared out of the reactor it will work fine. However, when the CO2 stopped running last night the water went clear so I don't think that there is a problem with trapped air/CO2.

2) It's been suggested that the flow may be too fast and the bubbles are simply cruising out the bottom. This appears to be the case, but there are others running the same system as I have without issues (i.e. 2 inch reactor with Eheim 2236). If the bubbles can't fight the current, a fix might be to build a wider reactor but I'm skeptical that this is the case. Also, if the bubbles can't fight the current in my 15 inch long reactor tube, then lengthening the tube shouldn't change the rate either

3) There was a suggestion that the tiny bubbles that the diffuser produces are too small to be buoyant against the current and I should instead drill into the diffuser and stick the tube through as in the original Rex design. This could be the case and when I first started the reactor I saw the larger air bubbles thrashing wildly near the top. But I wonder if introducing larger bubbles would help as those larger bubbles would quickly be broken into smaller ones that could just sail down the tube as they do now. It's possible that moving the CO2 input to a simple tube/barb and putting in larger bubbles would help, though.

In an hour or so the CO2 will turn on. The reactor has been running with no CO2 all night so I'm pretty confident that there is no trapped gas bubble, etc. If it doesn't work well, I might start constructing another reactor or planning a mod to this one.

I have about a 20 inch length of clear PVC left over and I am having fun working with this stuff

You are over thinking this. If you want to try using a reactor to see if you will have no more bubbles entering your tank then make a standard reactor instead of mixing a reactor design with an inline diffuser. If you make a standard Rex reactor using the clear 2" PVC you will be able to see exactly what is happening to the bubbles within.

I can't see into my reactor but am guessing that the churning doesn't progressively break the CO2 bubbles into mist, if anything they all combine and then the CO2 slowly dissolves into the churning water due to the length of contact, not because each individual bubble gets broken up to be progressively smaller before dissolving completely. Someone using clear PVC would have to chime in and let us know exactly what is going on inside their reactor.

You could also check out Tom Barr's reactor design which uses a thin plastic tube inserted through the top that ends about 2/3 of the way down the PVC tube as a way to input the CO2. This way the bubbles initially have to rise much further against the inflow. His design incorporates an optional venturi loop so that any undissolved bubbles end up back in the reactor until they dissolve completely. You can find info about this reactor on the Barr Report.

MrMoneybags said:

...something that just occured to me

when was the last time you cleaned your filter? maybe your filter is very clean so you have very good output GPH...I havent cleaned mine in a few months so reduced flow = more efficient reactor??

Click to expand...

My filter is pretty clean, and I intend to keep it that way

rickztahone said:

If you drill a hole you would have to take off the connection you have going, that might have been obvious but just making sure. Once you drill the hole, with a drill bit 1-2 sizes down from the tubing, insert and you can add silicone on the outside. As captain said, some prefer to place the tubing a little lower than conventional but thats your call. With your situation I dont think anyone can tell you what will work and what wont but apparently this current set up isnt working, so why not switch it up? I honestly think its your inline diffuser but i could be wrong

Click to expand...

It all really depends on what, exactly, happens in the reactor.

If the CO2 is dissolved due to the bubbles being constantly broken into smaller and smaller bubbles by the turbulence in the water, then those bubbles would presumably get so small that they would be subjected to the same current that they are now and would simply be carried away.

However, it might not be as simple as that. What if the mechanical 'shredding' of the bubbles isn't what makes the turbulence so valuable, and instead the turbulence of the water causes the CO2 bubbles to be much more rapidly dissolved regardless of their size. In other words, a big bubble get thrashed around in the water will be dissolved more quickly than a tiny bubble sailing along gently - then it could make sense to try the other technique.

If I do that, I am determined to put a hose barb on the side of the reactor rather than just stick the hose through. I don't why but I simply can't abide the 'just stick it through' technique