High CO2 Injection Rate & Marginal CO2 Saturation - The Planted Tank Forum
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post #1 of 3 (permalink) Old 01-22-2019, 01:58 PM Thread Starter
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High CO2 Injection Rate & Marginal CO2 Saturation

Hello all,

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?

Thanks!
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post #2 of 3 (permalink) Old 01-22-2019, 03:22 PM
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Hi @cqlink,

A lot of factors effect CO2 saturation (CO2 ppm) in a tank and the one you named, surface agitation, is by far the most likely. Another cause is surface area. The 125 gallon has a lot of surface area but there is nothing that can be done to change that. Is there any way you can cut down on the surface agitation for a few hours and see if the CO2 saturation increases (pH drops)? If so at least you know the cause.

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75 Gallon, 2X55W AH Supply CF 8800K, 1X 59W Fluval Plant (3.0); 45 Gallon Tall, 1X 46W Fluval Plant (3.0); 30 Gallon Long; Fluval F&P 2.0; 20 Gallon, 1X26W AH Supply LED; all with CO2 & (Calcined) Montmorillonite Clay
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post #3 of 3 (permalink) Old 01-22-2019, 04:24 PM Thread Starter
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I have a medium sized power head opposite of my return nozzles to promote flow/ eliminate any dead s[pots. I'll shut it down and monitor.

Thanks!
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