Needle Wheel & Drop Checker Readings

A drop checker measures how much dissolved CO2 is in the tank. But, a CO2 mist system delivers a lot of the CO2 as gas bubbles, not dissolved in the water. So, with a good mist system the plants will always have access to more CO2 than that which is dissolved in the water. I'm not sure if having 30 ppm of dissolved CO2 plus another 30 ppm (for example) of CO2 as gas bubbles is harmful to the fish or not. I suspect it isn't or people using heavy CO2 mist would have reported problems with their fish.

I'm thinking about that Octopus needle wheel pump too. One advantage it would have is that it adds a lot of water flow for better distribution of CO2 and other fertilizers to the plants, as well as giving good CO2 mist. The price is good too. But, I don't know if it is enough for a 90 gallon or not - my tank is 45 gallons.

 

I'm running a 1000 lph (264 gph) Gen-X needle wheel pump, and it's got some very nice flow. I'd say as long as you have a properly sized filter already in place, that this pump, and perhaps the Octopus as well, would be able to provide sufficient flow to a 4 ft tank. I believe the Gen-X is a few bucks cheaper as well, I got mine for a little under 30 bucks shipped to my door.

 

I use a Penguin Powerhead 660 as a CO2 distributor for a 50G tank without any issues. It is 175GPH. I have it setup just below my filter's output -- I think this helps the CO2 get distributed well. Two of the Octopi would surely work for a 90G. You have to go thru the trouble of splitting your CO2, however. One might work (perhaps you could even go up one model).

 

I find the drop checker (DC) accurate and useful, even with the powerhead method. Of course, you wouldn't want to place the DC directly in front of the powerhead. I place mine at just about the last place the flow reaches. I always have 30ppm (green).

I can't believe that I'm the only one, but almost all of my CO2 dissolves (at 3bps). There are some super tiny bubbles that you cannot see unless they are in the light and you stick your face right up to the glass -- I don't think they ever reach the surface. I do feed in my CO2 in a way that the suction from the powerhead peels off a thin layer of CO2, so I do not get big bubbles of CO2 hitting the impeller. I didn't even bother needle wheeling (nice verb, huh?) the impeller because it wasn't necessary.