Q: Where can I see the serial number on my Poseidon MKVI?

A: There are two ways of finding the serial number of your unit.
- When you wet the two wet switches on the back of the display, the display will show the version number of the firmware installed and the serial number of the unit in the lower left corner as XX XX. (Example: 06 54.)
- The serial number is engraved at the bottom of the e-module.
We recommend that you write your serial number down and keep it in a safe place as you need it to perform value changes on your unit.

Q: When I dive with my Poseidon MKVI, I get C1 warnings on my display. What is this?

A: C1 is short for Confidence level 1, meaning that the primary oxygen sensor produces a response that is outside the allowed parameters, at a sensor validation. As the sensor gives a response not regarded as correct, the unit chooses not to trust the sensor, thus the alarm. This also includes the case if a sensor gives the exact same PO2 value at two consecutive validations. Then the unit thinks the primary sensor is frozen. If the PO2 value is changed at the next validation (aprox. one and a half minutes later) the alarm will stop. All C1 alerts should be handled like a critical alarm and all instructions on the display should be followed.

Q: When I do the pre dive test, I keep getting a 49 error. Why?

A: An error on test 49 in the pre dive check indicates that the breathing loop is leaking. In most cases, it is due to the OPV on the exhalation lung not being closed or a damaged/missing o-ring somewhere in the loop.We recommend that prior to each dive, when putting your Poseidon MKVI together, all o-rings in the loop should be checked and lubricated.

Q: My Poseidon MKVI will not pass the 53 test during the pre dive check. Why?

A: Test 53 is the oxygen sensor validation test. If the pre dive test fails on this test, is because the primary oxygen sensor returns a value that is outside the allowed range, indicating a problem with the oxygen sensor.There are a few things you can do, to check if the sensors are bad or not:- Swap place between the primary & secondary sensor and run the pre dive again.- If it's cold, warm the sensors before doing the pre dive or do the pre dive indoors.- If you have put brand new sensors in to the unit, allow the new sensors to breath for 24 hours before you do a pre dive test with them.- Analyze the gas you use, to make sure the levels of oxygen are correct.If the unit continues to fail on test 53, replace one or both oxygen sensors.

Q: The pre dive test keeps stopping on test 55. Why?

A: Test 55 is the Service Interval test. When the Discovery is delivered, it has a service interval of 104 weeks. For each week that passes, this value is counted down towards 0. When the value is 0, the unit will not pass the Pre Dive ckeck.To reset the service interval value, you need to take your Discovery to a Poseidon Service Center.

Q: How deep can I dive with a Poseidon MKVI?

A: The standard Poseidon MKVI is a recreational non-decompression dive rebreather with a max depth of 40 meters.This means that the unit will guide the diver to stay above 40 meters and not get into a decompression dive.Should the diver go deeper than 40 meters and/or go in to a deco dive, the unit will alert the diver by using light, sound and vibration alarm signals and it will also support the diver all the way to the surface, even if it requires decompression stops. It will also work at depth greater than 40 meters but it's not recommended.If you want to dive deeper or with decompression stops you have the following options:40M Deco Battery - Allows you to dive to 40M with decompression stops.48M Deco Trimix Battery - Allows you to dive to 48M with decompression stops and trimix in the diliuent.60M Hardware/Firmware Upgrade - Allows you to dive to 60M with decompression stops and trimix in the diluent.

Q: Can I dive the Poseidon MKVI with Trimix?

A: Yes. You need to upgrade the standard Poseidon MKVI with the 48M Deco Trimix battery or the 60M Hardware/firmware upgrade. You don't have buy the 60M Hardware/firmware upgrade at once you can start out as a recreational diver and as your knowledge progress you can upgrade your Poseidon MKVI.


The Poseidon MKVI Rebreather was launched in 2009. It was discontinued 2014, when the new model SE7EN was introduced. The MKVI will still live for many years in the hands of the diving community. We supply spare parts, as many items on the MKVI and SE7EN are the same. We also take care of the customers and help with repairs of electronics and pneumatics. So if you find a used MKVI, buy it, dive it and have fun. Happy Days!