High CO2 Injection Rate & Marginal CO2 Saturation
I've a 125 gal. tank (approx, 90 gal water volume) with overnight (no CO2) pH around 8.1. KH = 5.5-6.0 GH = 8.0
In order to maximize CO2 diffusion, I'm running TWO external reactors through a Fluval 206 straight into a low level of my tank. Two returns from my sump push water over the CO2 outlet in my tank. As you can guess, I'm not seeing any micro bubbles. Problem is very slow plant (vals, hairgrass and swords) growth. I know hairgrass grows slow but past experience with a variety of vals tells me they should be growing a lot faster.
In order to drop pH from 8.1 to around 7.5 (yes, I know measuring pH drop isn't the most accurate way of assessing CO2 saturation levels), I'm running a very steady stream of CO2 from my 5lb CO2 tank. I can't estimate bubble count. In order to reduce pH further, I have to open my regulator needle valve almost all the way. This empties my CO2 tank in two to three weeks. At $25 a refill, I can't afford to keep doing this.
I'm guessing I'm losing CO2 through gaseous exchange at the surface. Water turbulence at the top is not fast, however. The glass top sections of my tank are open only near the tank overflow.
If the gaseous exchange is the root cause of this problem, Any ideas how I can slow down the exchange to maximize CO2 saturation?
I've seen evidence on Tom Barr's site suggesting running misters instead of reactors may help(?)
Any other thoughts?