Okay, for those here at HCA who know me; you know I couldn't resist jumping in on this one.
It has been asked what is the purpose and benefit of the 5-1 mix. Well, even on a "white sand beach", it is not pure sand, but a mix of sand and decomposed (or decomposing) organic material such as dead fish (and other critters), fruit, plants, etc. So it is safe to assume that almost all species of land hermit crabs (in the wild) live in substrate that is a mix of sand and organic material.
Even handling EE versus sand, you can see that the EE is much more moist, so that does help the humidity. In my experience, adding the EE to the sand helps the humidity of the
substrate, not so much the tank (as it does when it's pure EE). It also can help hold the sand together when the sand itself starts losing it's moisture, allowing less room for "error" if your tank humidity should drop.
Having the mixture also cuts down on the "dustiness" inherent in pure sand in your tank; a benefit to critters with modified gills.
Also, it has been established that EE can biodegrade molters as it decomposes so much faster and holds in more heat than sand (kinda like a compost pile). Many people have noticed a dulling of the shells of crabs who spend their time in straight EE. If it's doing this to the shells, imagine what it could to a gooey little molting crab.
I have used straight EE and had successful molts, and I have used straight EE and had a crab die in it trying to molt. I have lost a crab in the sand mix (though not from or while molting) and the crab who died in the straight EE was far more decomposed in a much shorter time. That was all the convincing I needed, personally.
I have also observed my crabs' digging habits in both mediums. I noticed in the straight EE, they buried, and that was it. They had a hard time keeping a "chimney hole" (as I call them) and they were never able to have tunnels. They simply buried covered up. In the mix, they can build a little tunnel down as deep as they want that if they
choose not to close it in, you can look inches down into the hole and see them in there. When digging, the crabs actually moisten the "walls" of their tunnels (like building a sandcastle) and the EE just doesn't stay where they put it like the sand or sand mix does. Like I said before, having the EE mixed in will help the sand stay stuck better (it bonds better to the sand than to itself, maybe?) even when the sand is not at an ideal moisture level.
Although I have heard of plenty of people succeeding with only sand in their tanks it's the straight EE tanks that should be avoided. Though there are people who say they haven't had any problems with it. (Personally, I think some of them just don't want to believe that is the problem, so won't give totally accurate data, but that's just me.)
I think the point in telling a new person to use the mix is in the interest of passing on the best information that person has available to them for passing on. I don't think there is anything silly about trying to be as helpful as possible to a new person. Like Sue, I too strongly believe the mix is the best idea and I implicitly trust Exotic Land Hermit Crabs, so if they say go with a mix; that's what I'm gonna do,hh.
I think the 5-1 ratio is just a good idea of the mixture. Does it have to be PRECISE? Probably not. In fact, mine (until recently) was actually probably closer to 4-2, but I will never go back to straight EE. I personally don't mix the oyster shells into the substrate, preferring instead to offer it in the food (along with other sources of calcium, of course
) so that I can keep (a little bit) better track of who is eating it and how much is being eaten.
Is the 5-1 the ONLY or BEST mix? Probably not the only, but the people I trust the most say it is the best,hh. Are there other important issues to cover for new crabbers? Absolutely. However, when it comes to substrate, it is one of the most fundamental components in your tank and the HARDEST to change if you change your mind or discover a better idea, so....I do think it's an important thing to cover in the beginning since you start your tank by putting the substrate in first.