Need help with CO2 for a big tank



I'm helping a local fish store set up it's 1st CO2 system on their 6 foot planted display tank. I'm not sure of how many gallons, but I assume 125-150. I'm trying to spread the CO2 gospel, so I'd like to see it succeed in a big way.:) I’m worried about getting a high enough CO2 level in this big tank.

The CO2 will come from a tank and regulator used for a calcium reactor on a salt water tank that has two unused needle valves/bubble counters. I'm donating a homemade in-line PCV/bioball reactor I used on my 75g to good effect and/or an extra Kent venturi I have. To power it, they want to use either a Fluval 404 or a pump rated at 295g/hr they have lying around. I vote for the Fluval since the tank is probably under filtered anyway and it’s rated at 340g/hr for better circulation through the tank. I planned on having the input and output placed at opposite ends of the tank for better distribution.

This is where I think I need help - how to place the venturi and/or reactor to get the most efficient dissolution of the gas. I’ve been using a Kent venturi on my own 75g on the output of a canister filter and I can see many fine gas bubbles come out of the spraybar, so the gas isn’t completely dissolved. For this big tank, I was thinking of putting the venturi on the input of the reactor after the Fluval to get better dissolution.

Alternatively, I could use the venturi to inject gas into the input of the Fluval, use it as the reactor, not worry about the impact it might have on the biofilter, and eliminate the PCV reactor. This would increase flow for better circulation though this 6 foot long tank.

Another potential problem is that the gas supply hose from the needle valve will have to run about 15 feet. I was going to put a check valve right before the injection point to stop the gas supply tubing from filling with tank water, but I’ve never run a CO2 line this far and I was worried that might be problematic.

One other thought would be to use the other available needle valve and install two separate systems - one using the reactor & Fluval and one using the venturi & pump.

What do you think? Can this work?



Tom Barr

Staff member
Jan 23, 2005
I'd vote for the last option, use 2 valves to drive the reactor and venturi.
Then you can weigh which does best for the tank.

Use less light for the plant tank BTW, suggest they use the T5's(say 6x 39W).
They can grow anything they want with this.

Tom Barr