I think you're right, Mikecc. And now that I know that it's hydrogen sulfide (H2S), and not methane, I can search it more effectively. Apparently it's still a problem and if for some reason a deep sand bed got stirred, as in removing sand to seed another tank, it's still a possibility that you could kill off your entire tank. So why do people use sand? It's not an effective filter if it's not getting oxygen to it like if the oxygen could be forced through the sand because we know that a lack of oxygen creates an anaerobic atmosphere. Is it possible that there are people on here with expensive, beautiful tanks that are a ticking time bomb? I'd like to hear everything that I can before I start my build.
The answer to your question is a chapter in a book, but I will attempt a short answer and hope that it is concise enough.
I have a tank that is 8 1/2 years old and it is always clean and I attribute that to a deep sand bed. I have never vacuumed the sand and I have never had nuisance algae grow on the sandbed.
You're missing something in the equation. If you have a deep enough sand bed, over three inches, you will not have a build up of H2S because there will be denitrifying bacteria to eliminate that. When you have a sandbed that is over 1/2" and under 3" is when you can run into problems.
I'm sorry I was going to take the time to answer your question, but I just really don't have the time. I HATE MONDAYS. I'm going to quote a book instead. This is a few paragraphs out of "Book of Coral Propagation" by Anthony Calfo. I highly recommend that every reefer read this book.
"The plain truth of the matter is that the actual depth is all that matters and sufficient product should be added to achieve your desired goal. Sand between 1/2 inch and three inches is usually not deep enough to reduce nitrate and yet too deep to be fully aerobic. In my opinion, it is a recipe for disaster and partly the reason why some aquarists have failed when employing static DSB or Jaubert style plenums. In some cases, the failure is simply the penalty for cost cutting and shimping on substrate depth.
Ultimately, I recommend six inches of fine aragonite sand (<2mm) as a minimum for optimal denitrification and mineral support from a DSB. The dissolution of sand is quite advantageous as aragonite contains balanced ratios of elements such as calcium and carbonates. These compounds are liberated when the substrate becomes acidified. The availability of growth-supporting minerals from dissolving aragonite sand is a significant benefit, as the media has a "half-life" of about 2 years or less (fully half of the sand bed will dissolve and can support coral growth with little or no additional calcium supplements.)
Another interesting benefit of deep sand beds is the competition of the living substrate with nuisance algae for nutrients. Nitrifying bacteria in the oxygenated upper region of the substrate will compete with pest organisms for ammonia and other nutritive compounds in the water. There are limitations to the process, or course, and aquarists who have suffered significant blooms of algae that they wanted to blame o the sand bed should consider their overall system husbandry. It must also be noted that success with deep sand beds for some have been attributed to partially open systems for better overall water quality."
There's a lot more information I can give you on DSB's besides nitrate reduction and nutrient control. Like how important the microfauna is to the overall health of a saltwater tank. Or how it has been well documented by leading aquarists that stir their substrates to feed corals with dissolved organics, bacteria, and plankton when keeping very challenging corals.
There's a long list of how beneficial a DSB can be to a saltwater tank. But I can tell you through personal experience of keeping saltwater tanks for around 25 years that I have had sandbed of different depths and also no sand. IME the tanks with the DSB's require almost zero maintenance and are far and above the cleanest and healthiest of the tanks I've kept.
and I'm fixing to add a refugium that I wanted a DSB in. 
having a reef tank just isn't simple as to what's best & what needs to be completely avoided.