Overshooting pH with the Tunze 7074/2 controller

[Charley2015]

Hi,

I'm trying to use some Tunze equipment as part of a scientific experiment, but I'm having trouble getting the equipment to do what I need it to do. Any advice you could offer would be a huge help!

I am using a:
*Tunze pH controller (7074/2),
*Tunze CO2 diffuser (7074.50) and
*Tunze CO2 regulator (7077/3).

I want to use the system to inject 100% CO2 into a 12L seawater tank to achieve pH 7.7, but the system keeps over shooting the set pH.

I've tried altering the regulator valve, the motor speed, and the controller timer but nothing seems to work. Any advice on what I am doing wrong?

 

[rvitko]

I would set a very low bubble count of about 1 bubble a second or every 2 seconds. I would set the controller timer to the maximum delay, this way it meters and waits the delay time to gauge the effect. I suspect since the volume of water is so small the residual CO2 in the diffuser is causing this effect. In a worst case scenario I would replace the diffuser with a simple diffuser that does not trap the bubbles (one that is like a very fine airstone) or I would drill a vent hole at the top of the diffuser so the bubbles can escape and do not recirculate for as long.

 

[Charley2015]

Thanks so much for your help, Roger. I switched to a fine air stone and set the bubbles to a low flow rate as you suggested, and that has solved the problem. Thanks again!

 

[rvitko]

Thank you!