Rex grigg reactor questions. - The Planted Tank Forum
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post #1 of 4 (permalink) Old 09-12-2015, 12:43 AM Thread Starter
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Rex grigg reactor questions.

I am going to build one to test it out vs my other method of diffusion but I want to make sure I understand the concept.

1. Longer the tube the better
2. Water enters the top and co2 stays on top until fully dissolved
3. Co2 enriched water leaves out through the bottom while co2 stays on top and doesn't leave the reactor.

1. What prevents a pocket of co2 from forming at the top of the tube?
2. How long should I make one for a 75g? 30"? Bigger?
3. What diameter is best? 1" or 1.5 or bigger?
4. Do I need to inject the co2 into the side of the reactor near the top OR can I have it run into the top of the reactor through the water by using a T in the outlet water line from my canister?
5. Any other key info I am missing?
6. Any good build threads with pics?


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post #2 of 4 (permalink) Old 09-12-2015, 01:17 AM
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1. Within reason but I find it is a combo of what diameter and length as well as what filter flow the CO2 is working against.
2. Kinda /sorta? The Co2 injected nearer the top meets the incoming water. This tries to force the CO2 bubbles down while they try to float up. So the best is that they go round and round, up and down but at some point the bubbles get too small to go up against the current and then do pass on out into the tank. Ever thought about how hailstones are produced? Same thing in reverse! Hail tries to fall down and get pushed up until they get too large and fall out.
3. Not much of a bubble or cloud of gas at the top because there is a constant flow of water going down. One reason for adding the CO2 in the center of the water flow so that it meets the stronger flow of water rather than the slower. less steady, flow near the edge. Think of the water in a river where the flow along the bank is slower than the stream center.

I find using Eheim 2217 on 75 gallon tanks, a single 1 1/2" with 18" of pipe and then adding a few fittings gets me total 21" and it never gives me any fizz in the tank or noise. Seems about right size to me.
Side or adding it at a fitting inline would seem to be much the same. I drill the side just to avoid using more fittings. Each fitting will decrease the filter flow a bit due to the way fittings are built. A fitting that is 3/4 on the outside is way less on the inside where the water runs. Too many fittings and the flow goes down more than we might want.
No good build posts but a couple ideas? Keep flow up as much as possible by using minimum number of fittings. If it fits your stand, etc. a gradual curve in the tubing will slow flow quite a bit less than a 90 degree angle fitting. If you watch rivers, you can see water running somewhat like car traffic. Curves slow things less than right angle corners due to the "turbulence" caused in each case.
The way mine are built?

Tubing from the 2217 (not the 2075 that is seen) through adapters to cut it down to the right size to go into a threaded plug glued to a coupling. This is done so that the tube can be pulled into the center of the pipe without a fitting. An 18" X1 1/2" pipe with threaded tee at the bottom. I give up some flow to go with the 90 degree line out at the bottom. The tee has a flat plug at the bottom because they are flat rather than using a cap which is rounded and makes the reactor harder to stand up by itself. I search for the black plastic (ABS?) irrigation fitting at the bottom as I like the more secure grip it gives on the tube without using a metal seal like at the top. I lose some flow but I'm willing to go with that.
I find no need of the purple primer when the pipe is new and not used outside when cold or wet. The normal glue softens the PVC fine when it doesn't have a lot of oxidation built up on it. If it's old pipe, use primer. USE fine grit sandpaper on all joints before gluing them up. Makes them fit the socket better as well as glue better. Test fit before gluing and don't work near flames. Outside is nice to avoid headaches?

Just my spin and there are hundreds of others out and about!!

Last edited by PlantedRich; 09-12-2015 at 01:22 AM. Reason: typos!
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post #3 of 4 (permalink) Old 09-12-2015, 02:02 AM Thread Starter
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The for all the great info.

Isn't the idea of having a lower flow better? More dwell time? Less chance of an pushing out bubble?

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post #4 of 4 (permalink) Old 09-12-2015, 03:21 AM
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Depends on how the tank as a whole will operate. If the filter is plenty to handle the load and the flow to get things moved around to the pickup is good enough for what you want to see, the decrease in flow could lead to longer dwell.
That's part of where we all have different needs for our tanks. Some will want all the flow they can get plus wish for more. Those folks will begrudge ANY loss of flow. I tend to be in that group and work to avoid it by sizing the reactor and choosing the fittings to do the best I can on avoiding loss of flow.
One thing that leads me to that group of thinking is that I use the flow to decide when filters are getting around to needing cleaning. Flow does drop off as filters become clogged so keeping the flow up s just kind the right feel for me.
But that gets back to sizing. Once the CO2 is totally IN the water , rather than bubbles, I don't see it reforming bubbles or doing anything that we would see in the tank water. So making the reactor larger either in diameter or length would seem to be better than cutting the corner a bit to sharp and not having it large enough-- as long as it fits the space available.
I think my first reactor was used on the same size tank as Mr. Grigg's and his info was still on the net so I just went with safe and it worked so well that I never really got too far off his plan. The old " don't fix it if it ain't broke", idea?
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