Which CCR Rebreather

The ISC Pathfinder vs Poseidon MK6

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Poseidon MK6

After the JJ-MEG comparison, friends and students have asked us to do a review on the so-called rec – tec hybrid rebreathers the ISC Pathfinder and the Poseidon MK6. So which CCR Rebreather? The label is perhaps an unfair one because as two of the most progressive CCRs on the planet they bring to the table unique concepts that just so happen to make them considerably easier than others to learn.

Poseidon MK6

Let’s start with the oldest one and the female, the Poseidon MK6. Why female? without intended pun, these rebreathers can be quite temperamental. When upset, it takes some insights from the diver, to find the issue, treat it with a lot of TLC and it happily gets you through a 3 hour 100m dive.

That said, the Poseidon being temperamental is no bad thing. The sequence of 55 primary tests and subtests which are automatically run on start-up, manage to catch many problems a typical earlier generation CCR diver would likely miss.


The Poseidon is a production unit, meaning moulds and extrusion profiles literally pull the unit out of alloy and polymers (aluminium and plastic). this means a high investment, but lower production cost in the end. and a very light unit.

Poseidon teamed up with a few specialist specialists and with the fail-safe success of the earlier cis-lunar rebreathers from Dr.Bill Stone, the Mk VI was born. The unit looks like it is; thin metal and light plastic. This is likely the lightest ccr on the planet.

The scrubber is pre-packed by Sofnodive and the cartridges are neat and easy to use, but quite pricey in most countries because of taxes and shipping as they are made in the UK. However, availability is good thanks to the overwhelming success of the roll out worldwide.

Quite a few technically minded divers travelling to remote locations now opt for the Tecme re-packable scrubber, which seems to do a good job. This is an untested after market product that cannot be sold in Europe. One should check if their dive insurance covers an altered unit.

The counter-lungs of the Rebreather Poseidon MK6 are front mounted and have the over pressure valve on the right exhalation counter-lung. The flow direction is clockwise. The counter-lungs, loop and t-pieces look and feel light build quality, but to date, we have not an anything broken whilst having the unit (harshly) subjected to hundreds of dives. A benefit of the lightness is that the loop sits surprisingly easy in the mouth.

Simone Reymenants Maldives
Simone Reymenants Rebreather Diving Poseidon

The work of breathing on the Poseidon Rebreather is quite good. We would rate it in top 3 of lowest WOB. Poseidon updated their Mark VI to the Se7en with some nifty features. the unit now boasts a multicoloured HUD and bluetooth in the handset, so no more infra-red dongle. The HUD does not allow you to check PO2, it is only a status indicator.

The mouthpiece has been upgraded to  ‘click’ OC or CCR, so no more in between positions. The manufacturers doubled the performance of the CPU and it is now capable of handling complex mixed gas dives.

The cover , which opens like a car booth is a very nice touch and doesn’t change anything to the size/diameter of the unit. It still fits in my hand carry (without the tanks).

Where originally designed to feed the recreational market, Poseidon received too much pressure from the technical diving world to make a unit for that market.

But it still had to be foolproof. Engineers understand the amount of what-if’s and scenario’s have to be built in and re-designed on a continuous basis. Therefore the SE7EN has a built-in error reporting log every time you connect the unit and you’re online. If you’re lucky and one of the service techs in Sweden is online, they can actually live, try to solve the problem on your unit.

Poseidon boasts the controlling resource algorithm, enabling two different algorithms to interact and take over as soon as the BOV is switched for when of a bail out. the processor senses this and will instantly re-calculate your decompression requirements. Only downside is; one gas only.

However, divers who find themselves bailing out to multiple gasses will have planned the dive appropriately for such a circumstance and would shift to each bail out tables or back up computers. After all, one of the contingencies planned for is total electronics failure.

The main algorithm is DCAP, by Dr.Bill Hamilton who also wrote the WKPP tables. The unit has two oxygen cells and does continuous cell calibration, current limitation, 2 point linearity checks etc all by itself. This tends to give headaches to divers not having the right mixes, old or wet cells, or simply dropping too fast, which, from a safety perspective, is not a bad thing.

New to the Se7en is also the quick connects on the head. there is no longer a need to send in the entire e-module, independent items as the HUD etc can be unplugged and replaced.

The unit can be ordered as a recreational unit (all gas injection ports on the counter-lungs are blocked off) with a 40m no deco battery and a recreational BCD, or as a full-blown tech unit with off-board Dil and Oxygen fittings, tank inversion set and a 100m trimix battery, a wing and a back plate and an optional 3rd cell for 3rd party computer monitoring.

Overall the unit dives nice. there’s quite a lot of straps and buckles, but the hardcore techies will easily replace those with a clean back plate and harness. the trim is one of the best as long as the tanks are upright. Inverting the tanks to easier reach the valves will make trim harder

The Pathfinder from ISC

The Pathfinder Rebreather is the little sister of Interspace systems workhorse, the MEG, a robust and technical rebreather. The production came after the quest for a lighter and easier to use CCR was opened.

Pathfinder Rebreather CCR ADV
Pathfinder Rebreather CCR ADV

The pathfinder has 3 Subcon wet connectors on it’s head where all the instruments can easily be plugged in and out; a)primary controller, which was recently replaced by a full multi colour display, deco upgradable in the near future, b) optional Petrel monitoring computer, and c) a fully independent 3 colour LED HUD, allowing you to read the Po2 of all cells at all times.

The unit has 3 cells with voting logic, and the air only calibration literally takes seconds. The pathfinder can be mounted on any back plate or harness, but the ISC Tetradon wing is a winner in my opinion; after 1000 dives, it has never failed me and , despite having tucked away bungees and a slightly odd shape, the trim and durability is amazing. One nice feature for the recreational traveler is the option of having all the Dil off-board; a 1L tank of oxygen is onboard. The Diluent is then connected to any off-board cylinder with a Swagelok QC6 quick disconnect.

Pathfinder from the top
Image from top Pathfinder

The unit is rated to 60m. It has been taken to well over 100m with fantastic breathing characteristics, but because the scrubber bed is thinner than in most rebreathers, the risk of CO2 breakthrough at high breathing rates at great depth becomes a real danger, hence they kept the limit to 60m and that is the depth of the CE rating. Divers should consider this not to be just advice but the absolute rule. The Meg remains the deeper diving CCR from ISC.

Interesting about the Pathfinder rebreather is that all main electronic components  are plug and play. computer, controller and HUD can be plugged and unplugged under water by means

Pathfinder CCR

of the wet connectors. Inside the head you find the propriety ISCan bus interface; e-module that fits inside your fist, can be unplugged in seconds, as does to the solenoid, sensor carriage; the entire head can be stripped in a matter of minutes and specific parts replaced in the field without the need of sending in the entire head.

Options the diver can choose;  front mounted lungs or top-of-the-shoulder-lungs, BOV or standard mouthpiece, petrel as secondary handset, oxygen only or dil and oxygen, steel tanks, alley tanks etc. This is quite a sturdy unit. only downside is that the wiring in the head is quite exposed and having a flood can damage contacts and wiring.

The anodizing of the aluminium can along with the use of a steel radial scrubber has led to some instances of corrosion where any moisture has been left in the can for prolonged periods and users should take to properly clean after daily use.

The trim is like any CCR with inverted tanks; it’s hard in the beginning. The Tetradon wing helps.

 Conclusion Which CCR Rebreather

The comparison between a Poseidon and a Pathfinder is simply impossible as the two are completely different units with unique approaches to expected user behaviour and needs.

They do however share some commonality, that they are both excellent for travel in a world where weight limitations and excess baggage charges are a harsh reality.

Poseidon’s offering has grown up to be the most advanced CCR in the world with full ability to undertake some serious diving with little interaction from the user to fly.

ISC have produced a robust, easily fixed in the field  unit with a highly advanced CAN system. Many of the traditional user overrides available to it’s larger stable mate the meg remain available.

Whichever you choose, both are highly capable and safe purchases.

Poseidon MK VI CCR
CLICH HERE FOR Poseidon MK VI info
CCR Megalodon Training

We have attempted to put forward an honest review, from our experiences, but note that in no way we are representing the manufacturer nor are official technicians. Some technical details, facts may be wrong or outdated, simply because we have not been explained the entire manufacturing process by the above companies which is, admittedly our neglect for not popping by the factory. So please feel free to correct us and we’ll instantly unfried you. =)

Ben Reymenants and Daren Marshall