Editor’s note - This is meant as an easy to comprehend guide for the novice to CO2 equipment. There are many a more detailed and in depth articles on the net dealing with this subject. The focus here is to explain in a manner easily comprehensible and without bewildering technical jargon. In this guide you will see me referring to EOTD and you may have heard or read of this before, wondering what exactly the end of tank dump phenomena is and\or why it happens? Simply put, it happens when the liquid in your CO2 cylinder runs out, resulting in the cylinder pressure decreasing and the output pressure increasing to where average hobby kit may become unstable. At this point all remaining CO2 gas gets dumped, potentially gassing your livestock. Scary stuff huh? Don’t worry, if you take preventative measures as I’ll be making mention of further in this guide, you will hopefully never experience this phenomena. For now let’s have a look at the various different types of regulators commonly seen in hobby. The Preset: A simple pressure reducer. These are among the most affordable regulators and what most hobbyists use and LFS stock. Unlike a working pressure adjustable regulator, the preset works on a very simple design that reduces CO2 cylinder pressure to a factory set non user adjustable pressure. When considering a preset, one should take into consideration the means of diffusion. For example, an inline atomizer requires much higher pressure than a reactor or glass\ceramic or lime wood diffuser. The latter can be driven on very low pressure, however an atomizer may require up to 45PSI (brand dependent). It is therefore important to purchase one capable of driving the greater number of diffusors on market or at least the means of diffusion you’ll be using. Being on the budged side of the pressure reducer world, these are generally paired with equally budget needle valves and solenoids and often no over pressure valve (RV). The few that do come with over pressure are generally fixed (i.e. non replaceable). It may also only come with one (HP) gauge that indicates the cylinder (high) pressure or none at all (not recommend). Most important thing of note is that with the average off the shelf preset there is no means of preventing the end of tank dump phenomena other than shutting down and refilling before CO2 cylinder runs empty. Thus the chances of gassing your livestock are more probable when using the average hobby preset regulator and even more so on the ones without high pressure gauge to provide warning of cylinder emptying. Note the preset has no pressure adjustment knob and also does not have a typical diaphragm as pressure adjustable regulator would have. The Pressure Adjustable Regulator: (See image and description in second post) A proper regulator with diaphragm\s and single or dual stage chamber\s. These are generally significantly more expensive than a preset and currently still not as readily available in LFS as should be. Since these are working pressure adjustable, one can simply and easily dial in required pressure, giving the hobbyist more control of whole loop stability as well as greater choice of diffusion method (kit dependent). When considering an adjustable pressure regulator, it again is advised to purchase one with over\pressure relief valve (most do have). Unfortunately some single stage regulators too may still suffer EOTD - the end of tank dump phenomena that only a dual stage regulator can completely and solely prevent. However, when using a quality single stage pressure adjustable regulator with good needle valve, you will significantly reduce the chances of ever experiencing the wrath of EOTD. The Dual (2) Stage: Exorbitantly expensive, but may be a good investment for those who spend months away on business or holiday and just want that extra peace of mind, as unlike the others, a dual stage is designed to provide consistent CO2 supply until the cylinder is completely empty, thus eliminating any chance of EOTD. The video below provides better description than what can be put in words or diagrams. The “Flow Regulator”: The cheapest of the lot - both in price, design and quality. It too generally either comes with one (HP) gauge that indicates the cylinder (high) pressure or none at all (again, not recommend). Same EOTD precaution apply, which is why the non-gauge variants are not recommended. Unlike the better hobby grade pressure regulators, these also generally do not have any form of over pressure valve and thus the chances of catastrophic (in the event of) failure are much higher with this type of “regulator”. *Pics, vids and diagrams not my own. All credit to original owners.