I'm setting up a new 125 gallon tank and had some questions about co2 reactors. Since I have no experience with these I bought one from Nilocg rather tahn try and build my own. I've got it all set up now, hooked up to a fluval fx4 in an empty tank to experiment with it.

A few things I'm wondering...

1. How should I position the co2 tube in the reactor? It's adjustable so I can put it in further (higher up) the water flow or lower down. I have no idea which is better...
2. How the heck do I tune this thing? From what I can tell just trying it out, it works by putting co2 bubbles into the reactor, which then want to float. But the water flow against the bubbles want to push them down. This gets balanced out so the bubbles just kinda float in the water flow gradually dissolving into the water. But from watching it, it seems like the Co2 bubbles stay in the water for a while leading me to think I need a VERY low bubble count to inject.

So I'm a total novice with this but any advice on tuning and dialing this setup in is welcome. Right now the tank is empty so I'm just experimenting while the plants are in a quarantine tank.

Are you referring to the above reactor? If so, there really is no "tuning" of the reactor itself. Don't think it really matters much on the black hose inside the reactor. You are correct in that the CO2 enters the reactor and floats to the top. The incoming water stream bounces the bubbles around until they dissolve. The "tuning" of the system is more related to the CO2 regulator and it's metering valve.
I can tell you on my 75g tank, the bubble counter is pretty much an uncountable steady stream of bubbles. Many on here with bigger tanks elect to use a flow meter vs a bubble counter - much easier to dial in the correct CO2 flow rate.

Nope not that one, it looks like this:

Good - that one is more appropriate for a tank of your size. Now lets see if I can explain the bypass valve :-) BTW, here is the one I designed back in 2015


The bypass valve is used to maximize the amount of co2 you can dissolve into the flow of water going thru the reactor. Lets say you have a Fluval FX6 canister filter with a huge amount of flow. If you run 100% of the flow thru the reactor (bypass valve closed) you will eventually get a fine stream of co2 bubbles exiting the reactor and going into your tank. If you open the valve 100%, there may not be enough flow thru the reactor to dissolve the incoming co2 fast enough and you end up with a big bubble of co2 at the top of the chamber.

Post 872 is the start of me adding an FX4 to my 75g tank

The black tube in the middle of the reactor is simply a way of getting the co2 into the reactor and directing it up to the top where the incoming water enters the reactor.

As you get used to your co2 system - tuning it will not be overly difficult. If you increase the flow of co2 into the reactor, you "may" need to adjust the bypass valve. This should at least get you started in the right direction.

This is from their site

Setup Instructions:

-Mount the reactor vertically(long side up)

-The water should enter the top and exit the bottom

-Start with the valve closed(parallel to the ground)

-When all the hoses are connected(filter and co2) run the reactor for 24 hours before making any changes

-If after 24 hours you are getting co2 bubbles out of the return pipe, open the valve slightly, then wait for 24 hours

-Repeat the previous step until you are no longer getting co2 bubbles pushed out of the reactor