Hello jmcgauhey, hold it, stop right there! Your best bet now that you've taken the Dolphin plunge(as I did once upoun a time)is to purchase a used unit and convert it to a KISS style CCR. If you don't know what this is, do a search of this thread or the internet. I say this because of the time, effort and money I assume you've spent to learn the Dolphin system. If you dive the unit the way you're taught, it's almost worthless-you will still discharge bubbles about every other breath, especially at shallow, critter friendly depths. To get the most out of the SCR Dolphin system you need to mismatch the oraffice for a slower flow rate than the actual corresponding nitrox mix, which is only optimal at 100 ft and beyond. BUT, in this configuration it's still much less efficient than a CCR, it's very imprecise without inline O2 sensor/computer interface, and you're asking for real trouble in normal recreational depths because of shallow water blackout. The reason for this will become apparent when you understand more about the physics/O2 fractions of an SCR. Don't trust me, do your homework. If you have bought a Dolphin, the good news is that they breathe better than other back mounted counter lung rebreathers and the conversion to CCR is simple and pretty cheap. If you have not bought a Dolphin, the Ray would be a better choice as it has over shoulder counter lungs and can also be changed to a CCR, but will breathe easier because of the optimal hydrostatic load of over the shoulder counter lungs. It's also lighter. There are 2 types of constant flow oraffices which are the main component of a conversion of the unit to CCR, one fixed and the other a variable needle oraffice which requires more diver attention, but which has more benefits: if you're photographing something and it takes a long time, a variable oraffice can be dialled down to flow so slowly as not to overtake your breathing rate and cause you to have to vent gas at a crucial photo moment to avoid floating upward. There can be problems with doing a CCR conversion to a Drager: most dive operators will not know the difference between an SCR and a CCR, but some will and they may be hesitant to let you dive on their boat with a modified unit. I can tell you that there are plenty of places, mostly in the South Pacific/Australia where others have converted their units to CCR's and they will be glad to dive with you. That said, I think it's still better to bite the bullet and go electronic CCR all the way from here on out. Your newly learned skills with still be relavant and you will have less hassel overall for many reasons, not the least of which is that nitrox is not always available as it requires a lot of hardware. O2 is never far away and requires almost no equipment to decant it to your CCR cylinders. Having started out on the Dolphin SCR, I can tell you I would have never chosen it over an electronic CCR had there been one worth buying at the time I decided to move over to rebreathers, and had known what I know now. Good luck.