# RE: CO2 loss through silicone tubing (was multi tank CO2)

```I wanted to post this one last time, since I caught some mistakes and
finally got the calculation “correct.”  I redid the calculation for low
pressure and high pressure systems; also for thick walled tubing.

Fick’s Law:
Flux = Permeability * Area * (Partial Pressure Difference)/ Thickness

CO2 Permeability silicone tubing		20132		(10^-10 cc-mm/sec-cm^2-cm Hg)
CO2 Permeability FEP tubing			5.9
(specs from Cole-Parmer catalog)

CO2 flow rate			1 bubble/sec	0.06 cc/sec (my measurement)
Room pressure			14.7 psi		76.0 cm-Hg
CO2 High Pressure Systems	15.0 psi		77.6 cm-Hg
CO2 Low Pressure Systems	  1.0 psi		  5.1 cm-Hg
Partial pressure of CO2 in air			  4.0 cm-Hg
thin wall tubing
tube wall thickness	1/32 inch		0.8 mm
ID of tube			3/16 inch		4.8 mm
Area 1 ft of tube		7.07 inch^2		45.96 cm^2
thick wall tubing
tube wall thickness	1/16 inch		1.6 mm
ID of tube			1/8 inch		3.2 mm
Area 1 ft of tube		4.71 inch^2		30.64 cm^2

Flux_hp_thin wall = 20131*10^-10*45.96*(77.6+76.0-4.0)/0.8 = 0.0173 cc/sec
Flux_lp_thick wall = 20131*10^-10*30.64*(5.1+76.0-4.0)/1.6= 0.00297 cc/sec

CO2 flux through tube
Tube length		thin wall, HP	thick wall, HP	thick wall, LP
1 ft			0.0173 cc/sec	0.00577		0.00297
2			0.035			0.012			0.0059
4			0.069			0.023			0.012
8			0.138			0.046			0.024
10			0.173			0.058			0.03

Percent CO2 loss (if aquarium use is continuous 1 bubble (0.06 cc) per
sec**)
Tube length		thin wall, HP	thick wall, HP	thick wall, LP
1 ft			22%			9			5
2			37			16			9
4			54			28			17
8			70			43			28
10			74			49			33

**The percent loss is a function of use rate.  For example, if you use 5
bubbles per second at LP with 4 ft of tubing, your loss rate would be only
4%.

```