OD of reactor dropping

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July 23, 2026 at 2:15 pm #1998

Kenny_G
Participant

Hi all,

I’m experiencing an issue with the OD reading dropping about 4 hours after inoculation. When this first occurred, I stopped the experiment, removed the reactor vial, and manually swirled it. The OD reading immediately increased but then started decreasing again after roughly 30 minutes.

My initial working volume is 20 mL, with a total final volume of approximately 22 mL including the inoculum. Based on these observations, I suspect the problem may be related to inadequate mixing and cell settling. At the time, the stirrer speed was set to 0.9, which is close to the maximum setting of 1.0.

I’m not sure what adjustments I can make to improve mixing and prevent the cells from settling. Has anyone experienced a similar issue or have any suggestions on how to troubleshoot this?

Any advice would be greatly appreciated.

Thanks in advance!

July 27, 2026 at 7:43 am #1999

harrison
Keymaster

Hey
If the stirring is not working it should be quite obvious – either there is zero sound when it is running, or there is a bouncing/clinking sound that is due to the stir bar “jumping” and not rotating. One way to test is to (without runnign an automated experiment) turn on one of the LEDs with the stirring and have a look from above and see what it seems to be doing.
If either of those is happening it would explain your observations. Best troubleshooting is to ensure you have the correct/recommended stir bar or swap out the one you have for another (identical) one in case it is faulty. Also make sure your tubes are getting right to the bottom to touch the heat plate when they are inserted. If none of that works it may be the stirring motor itself is not working…
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