I have a few questions for those of you who use or have used deep sand beds in your system. I understand that you should use at least 5" inside the tank, and have a very good circulation of water, some time ago I read from several aquarists that it is important to put the sand correctly with the granulometry of the aragonite or the sand that makes up the sand bed, I don't remember if the layer of aragonite with a larger granulometry should be placed at the bottom or on the surface of the sand bed, does anyone have an idea? or is this not true?
I've read this as well but don't believe it matters. I seem to recall it is more about blowing around in the flow and granular size. It has been a long while since I've looked into that so do not have a specific answer. I personally have a 3 to 6" sand bed using CaribSea Fiji pink and special grade aragonite. Both dry. 40lb bags. I mixed them together since I really didn't care one way or another mainly because I knew I was keeping Sapphire Damsels which tend to burrow under rocks.
I'm sure there is a reason though as you said but for me the DSB is more about it making me feel good rather than performing something specific. One of the things I read about is detritus build up and potential hydrogen sulfide build up. Detritus I don't care about. I get what I can and believe what I can't becomes inert over time. Hydrogen sulfide depends on what camp you fall in. Dr. Ron Shimek is knowledgeable so I would recommend reading some of his papers on it.
Only other thing I can think of is fish. If you have fish that are going to sand sift then finer grain on the surface makes sense. I know my Strombus snails prefer larger size. I've sprinkled some rubble I've created by braking apart larger rocks and the snails will lay their eggs there.
Apologies I don't have anything specific. Fish filter / sifting smaller grain.
Also for those who use a RDSB or have used it, is it possible to use this sand in another tank? Either completely or only some part; My assumption is that it could, but it would be releasing some toxic components wherever it is used, which would cause a new cycle practically when using it, what do you think?
With regards to remote DSB you could move it but I think it would be messy. My current display is 4 years old and part of a 40 breeder to 210 gallon upgrade. What I did was aquascape using the sand I noted above, took a cup or two out of the existing 40 breeder, and placed it in the new display after it cycled. Micro fauna, worms, whatever took hold in little to no time. Worm trails between sand and glass so I knew it was working.
I'm not really much of a believer of rinsing sand due to the amount of time, effort, waste of water, etc. Take a couple cups and toss the rest. I also know new substrate isn't cheap so rinsing will work but is going to take some time. Remember to dechlorinate if you use tap water.
TL; DR - I use DSB but mainly because it makes me feel good. I mixed my different sand blends. Search on Dr. Ron Shimek for sandbeds, dsb, detritus, etc. I've not run remote DSB. I take a cup or two and I toss the rest.
