CCR FAQ - Poseidon Se7en+

How much does a Poseidon Se7en+ cost?

A better wording of the question might be 'How much does it cost to switch from an open-circuit diver to a rebreather diver?' The price of the rebreather itself can vary significantly depending on configuration options. Plus there are usually additional equipment purchases depending on what existing gear can be re-purposed. Training, particularly if travel is required, will be a significant cost. For the US, we suggest budgeting a total amount of at least $15K and possibly as much as $20K.

What is the difference between the Discovery MkVI, the Se7en, and the Se7en+?

Released in 2006, the Discovery MkVI was the first Poseidon branded mass production rebreather targeted at the sport diving market. The Poseidon Se7en Classic, a model with significantly expanded capabilities including extended range technical diving, was released in 2012. The Se7en offered a detachable HUD, detachable HP sensors, and detachable display; providing improved field service since the customer could replace those components themselves. The Se7en Classic also had improved electronics with a more powerful processor supported substantially enhanced firmware features and hardware options, including support for Bluetooth and "dive-by-wire" CANbus connectivity along with hypoxic trimix diluents. Introduced in 2020, the Se7en+ electronics module was updated to include native support for Poseidon's optional Solid State Oxygen Sensor and an improved pneumatic block containing reduced parts count.

Can an old Discovery MkVI be upgraded to the new Se7en?

For several years after the Se7en was released, Poseidon also offered an upgrade path with attractive pricing to MkVI owners, but those offers are no longer available. Original MkVI units are occasionally offered in used equipment marketplaces such as eBay and social media, but given their twenty year old design these MkVI units are a poor value regardless of the resale price. The MkVI unit has reached end-of-life and is no longer cost effective to repair.

How long does it take to get a Se7en+ rebreather?

The rebreather Core configuration will usually available in less than a week after receipt of order. Occasionally, demand or logistics will cause brief stock-outs of the Core unit but delays beyond 30 days are rare. Accessories and spares are usually available for immediate shipment.

What is the rebreather training time and cost?

Standards vary depending on the training agency but a full "Poseidon CCR Diver" certification course that meets manufacturer requirements is normally about five days including academics, confined water and open water dives. There is wide variation in training costs due to a variety of factors, typically in the US individual instruction cost ranges from $1500 to $2500. If you prefer to learn about your rebreather at Dive Gear Express in Pompano Beach Florida, training can be organized to accommodate your schedule and rebreather courses run every month.

Can I buy the rebreather without training?

Yes, but purchasers won't be able to dive the rebreather until they are trained. Every rebreather requires formal, model specific, training in order to competently dive with the equipment; ordinary open-circuit training is not adequate. If the purchaser is not already a certified Poseidon CCR Diver, Authorized Poseidon Dealers will disable the unit by delivering the Smart Module only to a certified Poseidon CCR Instructor nominated by the purchaser.

How much does routine maintenance cost?

Budget routine maintenance costs of approximately $1000 every two years. The unit must receive a full periodic routine service every 24 months and the diver must replenish minor consumables such as lubricant and disinfectant from the maintenance budget.

What consumables are recommended?

The recommended consumables in the US are: Molecular Products Sofnolime Grade 797 loose 8-12 mesh granular carbon dioxide absorbent, Steramine for sanitizing the breathing loop, Tribolube 71 O2 Compatible Lubricant for O-ring seals, Caig Labs DeoxIT GOLD for cleaning electrical contacts, and for those units still using analog sensors then "R-22D" style compatible galvanic chemistry oxygen sensors such as the Poseidon 6010-206 or the Analytical Industries PSR-11-39-MD.

How much do the consumables cost?

As with all rebreathers, the major consumable cost is CO₂ absorbent. A self-pack granular absorbent load is about $30 and can typically can be used for several sport dives. There are other smaller costs such as gas fills. Keep in mind that for both open-circuit and rebreather divers, consumables costs are usually insignificant in relationship to the investment in the equipment, training and other diving costs such as boat charters and travel.

How long does the absorbent last?

If determining duration by wall clock time only then the absorbent duration is three hours. Divers tracking their CO₂ production by monitoring their oxygen consumption are reporting scrubber duration in the range of four hours. The duration in actual use depends upon many factors related to the individual diver and specific dive conditions. These are observations of what experienced divers are reporting and in no way suggests exceeding manufacturer recommendations or that novices should expect these durations. When in doubt, always discard the used absorbent and repack the cartridge with fresh absorbent.

What about the possibility of a 'caustic cocktail' with the rebreather?

For properly trained divers, inhaling a mixture of CO₂ absorbent and water while diving is very unlikely. The Se7en is a modern CCR design that includes several features to manage and remove water from the breathing loop. The 'caustic cocktail' is a concern from an earlier era of rebreather diving that has been overly dramatized, akin to the concern new divers express regarding 'shark attack'.

How available is the absorbent?

In the global economy, absorbents are sold and shipped all over the world. As a result, supply logistics for absorbent is becoming less of an issue. The number of dive shops that stock absorbent is consistently growing, and suitable absorbent is always available to order on-line for delivery to the diver or travel destination.

Is a pre-packed absorbent cartridge available?

Although the initial design of the Poseidon rebreather used a pre-packed absorbent cartridge called the "SofnoDIVE 797", as of late 2019 the manufacture by Molecular Products of those pre-pack cartridges was discontinued and they are no longer available. The Poseidon rebreather now has a reusable self-pack scrubber cartridge that is included with all new units and available as a separate purchase for use with existing units.

What about Solid State Oxygen Sensors?

The Se7en+ electronics module allows the choice of using traditional analog galvanic chemistry oxygen sensors, digital Poseidon Solid State Oxygen Sensors (SSO2), or a combination of both. The SSO2 offers the benefits of no need for periodic annual replacement with greatly enhanced speed and stability. Currently, the SSO2 is believed to have an estimated life of at least ten years (probably longer) but also costs about six to eight times more than a galvanic chemistry sensor. The SSO2 offers substantial improvements in convenience and reliability of oxygen measurement for divers. As of 2025, Poseidon recommends the Se7en+ be configured at a minimum with one Solid State Oxygen Sensor as primary.

Does the Se7en have a CO₂ monitor?

No. Carbon dioxide monitoring is a 'bleeding edge' technology that will begin to appear in recreational rebreathers in the next few years but as a practical matter the merits of CO₂ monitoring are unproven. Do not confuse a CO₂ monitor with the breathing loop temperature monitor or the scrubber temperature monitor offered by rebreather manufacturers. The temperature monitor does not provide any information or warning regarding actual carbon dioxide levels in the breathing loop.

What is the Smart Module?

Poseidon originally offered a selection of different Smart Modules(identified by their color) that provide power to the rebreather electronics and enable software features which allow progressively more advanced levels of diving. As of 2025, all new Se7en+ units include the Deep (aka Black) Smart Module that has no depth or gas mixture restrictions.

Which style of counterlungs should I choose?

Front-Mounted (FMCL aka over-the-shoulder OTS) vs. Back-Mounted counterlung (BMCL) technical configurations have subtle trade offs of one benefit for another, and the choice is more complex than can be answered briefly. Many professional photographers have a preference for back-mount, but for diving where performance is paramount the over-the-shoulder front-mount technical counterungs are preferred.

What about manual addition gas valves?

Manual addition valves are not a requirement on Poseidon rebreathers if the diver is willing to rely solely upon the electronics and automatic diluent valve to manage the breathing loop oxygen content and volume. However, most rebreather divers prefer having manual addition valves, and most training standards assume the rebreather is equipped with them. Poseidon offers a MAV pack that uses independently configured manual push-button valves attached to the breathing loop hoses and work with all available counterlung configurations. The over-the-shoulder front-mount technical counter lungs also offer an alternate option for traditional manual addition valves installed on the counterlungs themselves.

What BC should I use with the Se7en?

Although the Poseidon rebreather can be used with any type of BCD having ordinary tank straps, with a QMR option the Se7en supports most harness, backplate and wing (BPW) style systems that mount using posts on standard 11-inch centers. A wing designed specifically for use with rebreathers to minimize volume around the neck and head area is recommended. A minimum buoyancy of {30 lbs | 150 N} is recommended and more lift may be required depending on equipment configuration. Poseidon offers a harness, plate and CCR wing if the diver prefers to remain with a single vendor.

What cylinders should I use?

The rebreather will accept small 4 inch diameter cylinder sizes using standard 'inline' DIN valves. Aluminum 13 or 19 cubic foot (2L or 3L) capacity cylinders minimize the total weight, the rebreather may also be configured with steel 17 or 23 cubic foot (2L or 3L) cylinders. Most wetsuit divers find having the steel cylinders requires little or no additional weight and trim can usually be made perfect simply by slight adjustments to the mounting height of the cylinder.

What bailout should I use?

Although the Poseidon rebreather has an open-circuit bailout valve (BOV) built in to the mouthpiece, carrying independent off-board bailout gas supply and regulator on all dives is strongly recommended. Many rebreather training standards require an independent off-board open-circuit system with a minimum cylinder size of {30 cu ft | 4 L} for sport diving depths. Configuring the independent bailout first stage with an SPG and a low-pressure hose having a quick connect fitting compatible with the BCD power inflator and diluent manual addition valve is recommended.

What about the carrying handle, stand, and back cover?

They are optional and may be omitted for maximum weight reduction. However, adding the aluminum carrying handle is strongly recommended because it also protects the CANbus fittings and cable entries on the electronics module. The stainless stand is a popular addition if the unit is configured with cylinder inversion, but does add about {4 lbs | 2 kgs} to the total weight and can make the unit seem a little butt heavy for light wetsuit divers. The molded HDPE back cover is primarily cosmetic, but does provide impact and abrasion protection during transport.

What Se7en options are recommended for technical diving?

The M28 dive computer with a CANbus cable to connect to the Se7en along with the Deep Smart Module is now the recommendation for all diving. (The simple "paddle" display is not suitable for extended range technical diving.) Technical divers will need oxygen and diluent manual addition valves, along with cylinder inversion and should consider adding an in-line gas shutoff valve on the ADV/BOV gas supply immediately adjacent to the mouthpiece. (Just to be clear, this in-line shutoff is on the ADV/BOV diluent supply only; Poseidon does not recommend the use of in-line shutoff valves on the oxygen supply or any other location on the diluent supply.) Consider adding a third oxygen sensor to the breathing loop, along with a compatible backup dive computer for independently monitoring loop PO2.

How much does the Se7en weight?

Similar to a recreational open-circuit setup, a ready-to-dive Poseidon Se7en checks in with a dry weight of about {40 lbs | 18 kgs} for tropical wetsuit sport diving and is typically neutral to slightly buoyant in the water. However, the dry weight and buoyancy can vary considerably depending on the configuration and counterlung volume maintained by the diver. A maxed out Se7en for technical diving in a drysuit will be {50 lbs | 23 kgs} or more and significantly negative in the water.

What is the Se7en maximum dive time and depth?

Rebreathers carry many hours of breathing gas regardless of depth, so the dive time is rarely limited by gas volume. As with most rebreathers, the Se7en diver is typically limited by the duration of the CO2 absorbent, so multi-hour run time dives are routine. As with open-circuit nitrox diving, rebreather divers must also monitor their decompression and oxygen exposure; depending on the dive profile these may also limit the dive time. The Poseidon rebreathers are suitable for diving at all sport depths and the Se7en with the Deep Smart Module has been qualified to a depth of {330 feet | 100 meters}. Although the Se7en can function at depths well beyond sport diving limits, as with any extended range diving there are numerous additional considerations.

Is the Se7en capable of diving with mixed gases?

Yes, the Se7en with the Deep Smart Module can use either nitrox or trimix diluents that may be either hyperoxic, normoxic or hypoxic. Because the Se7en is a fully closed-circuit design, the use of mixed gas diluents is very inexpensive compared to open-circuit. However, use of anything other than normoxic diluent or diving outside of recreational sport diving limits requires significant additional diver training.

Does the rebreather take a long time to maintain?

Yes and No. Many rebreather sport divers, including Poseidon divers, find they spend noticeably more time on equipment compared to open-circuit because the rebreather diver must always be careful and disciplined about maintenance. If the diver has been habitually careful with their open-circuit dive equipment and treat their equipment with respect, experienced rebreather divers will spend only slightly more time with maintenance than with open-circuit.

Is the Poseidon rebreather Power-On-Self-Test troublesome?

The Se7en does not have any issues with the POST, which takes less than three minutes to complete from power-on to ready-to-dive. The early Discovery MK VI units were annoying about passing the positive pressure test and the sensor validations, but later revisions of the firmware corrected those issues although the reputation persists. Properly trained Poseidon divers can expect their unit will easily pass the POST every time.

How well does the Poseidon rebreather travel?

The Poseidon rebreather is travel friendly. A key design goal was to minimize size/weight and divers are able to travel by air with it as carry-on luggage in some circumstances. Regardless of the brand of rebreather it can be annoying to travel with cylinders because they are carefully examined by security personnel, and occasionally even confiscated. Many divers prefer to rent cylinders at the destination or ship their cylinders ahead.

How is the Poseidon different from other rebreathers?

All of the major rebreather models are good quality units. There is no perfect rebreather; they all have strengths and weaknesses that make each uniquely more or less suitable for a specific diver and their needs. The Poseidon Se7en is a richly featured and proven design with good redundancy from a well established manufacturer which favors the sport diver with intentions of continuing on to technical diving. It is also a uniquely automated design that is smaller, lighter and simpler to use than many other general purpose rebreathers. The Poseidon Seven is a robust eCCR choice that will take any diver as far as they wish to go in general sport and technical diving.

Is the Poseidon rebreather safe?

No type of rebreather can be said to be categorically safer than another. No rebreather is foolproof, and the fact remains that compared to open circuit there is a disproportionate number of rebreather fatalities, many of which have been attributed to diver error. The quality of training may be the most significant factor affecting rebreather safety. Safety while diving is controlled by the diver, not by their rebreather.