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CO2 & PH Controllers
Chuck Gadd wrote:
On Tue, 11 Feb 2003 10:30:53 -0800, Dave Millman wrote: However, about 3 weeks ago my dual gage regulator-needle valve system ran out of gas. It did an end of tank dump. pH dropped from about 6.4 to a bit under 6 before I noticed fish behavior and turned it off. So a needle valve does not prevent an empty tank pressure dump. What pressure do you run out of your regulator? Does your system have a check-valve? Where is the check valve located? CO2 tank side reads 800 psi, needle valve side set at 10-11 psi. I have a German check valve on the hose from the regulator to the reactor. The whole system came from M3 about 15 months ago. I've seen cases where the regulator pressure was set VERY low (2psi) and the resulting increase when the "tank dump" happened caused in a CO2 overdose. But if the regulator pressure is set higher, the needle-valve needs to be closer tighter, and when the output pressure rises, the needle-valve still limits the CO2 and prevents problems. Additionally, if there is a check-valve located after the needle-valve, the needle-valve often has to be set at a higher rate in order to overcome the resistance of the check-valve. Some check-valves cause problems, others don't. This is really interesting. In between my last post and this, I was up at a fish store that told me about a fish die-off they attributed to not turning off the CO2 at night. I looked at their tank: needle valve, no cover, lights suspended 8 inches above the tank, no chance of CO2 being trapped above the water and displacing O2. I told them it was unlikely that the night time ph drop killed the fish, and asked for more detail. They told me it happend three weeks ago, pH measured below 6 when they saw the dead fish. Then they said they had just about been ready to change the CO2 tank, because it was almost empty before the die off. This is exactly what happened in my tank, except nothing died (they did stop eating for a day, though!). So I have two separate experiences that the CO2 rate through a needle valve system can rise when a bottle gets empty. What does the CO2 triple point diagram say? Does pressure increase when the last liquid is gone? |
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