CO2 Injection with Fluval FX4

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Aquarium Advice Apprentice
Jun 24, 2022
Hi all,

I've read through many of the posts here, and other sites. I'm not finding what I'm looking for. So hopefully someone here has all the answers!

I have a 90 gallon tank with various community fish in it. I also have some plants in it that are struggling. I'm in the process of acquiring all of the equipment for CO2 injection, but I've run into a problem. First, here is what I have so far:
10lb CO2 tank
CO2art Pro-SE series regulator
CO2 specific tubing
CO2 checker
Bubble counter
Check valve

The piece I'm stuck on is the diffuser/atomizer/reactor. I have been doing a lot of research looking for something that will fit my Fluval FX4. These canister filters have 25mm (1") hoses for the intake and outlet hoses. Every reactor and inline atomizer is either 12/16 (1/2") or 16/22 (3/4"). I can't seem to find anything that support 25mm (1") tubing. I have seen 1 inline atomizer made by JBL. Reviews aren't so good.

I have determined I don't want an in tank diffuser spewing bubbles. I want something inline, or separate if it needs to be.
I think I'm to the point where I need to build one. I'm not opposed to doing this, I just want to make sure whatever I use, is good quality.
I've read numerous posts from people saying that they simply bought a reducer, and reduced the flow from 1" tubing down to 3/4" tubing. I won't do this as it's reducing the effectiveness of the filter. I've seen some with bypasses and flow valves to adjust the flow in the bypass. I'm not sure I love that idea either. I ran across Rex Grigg's post on the reactor he built. There are quite a lot of people who reference the "Rex Grigg" style reactor. So I'm guessing it works well.

So, to my questions.....
1. Does anyone know of a factory made inline atomizer or reactor that fits a Fluval FX series filter (25mm fittings)?
2. If I do need to go the DIY route, does anyone see any problems with changing the threaded ports from 3/4" to 1" to match the filter?

Im not really knowledgable about injected CO2, but i do know connecting anything onto fluvals ribbed hosing is a bit of a no go. Even things made by fluval that connect inline to their ribbed hosing, like their UV steriliser, won't connect to the larger hose used by their FX series. Even if you find something compatible with the hose diameter, it probably shouldn't be attached to ribbed hosing.

I have heard of people cutting the ribbed hosing and using adaptors to insert a section of standard hosing so that inline heaters can be installed. You can also remove the ribbed hosing altogether and use standard hosing instead, but you would need to replace the intake stem and output nozzle because standard hosing wont bend around the rim connector like the ribbed hosing.

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