Before discussing the issues of deep sand beds you should review
Robert Toonen, Ph.D. article.
http://www.advancedaquarist.com/2005/6/aafeature
If you want to design an experiment you have to limit your variables
and detail the hypothesis.
For example
DSB create more hydrogen sulfide than other sandbed types.
This question may already be answered (see article)
DSB hold toxins that will later be released.
This would have to be further defined. What type (phosphates?heavy metals)
How long?
DSB need additional organisms to work properly. This is more difficult to define.
What does work properly mean? What organisms ? What density?
What controls would you use? Regular sand bed, no sand bed, no treatment
How many treatments to be significant?
Ex. DSB hold phosphates that will later be released.
Just for a minimum you might go with 12 tanks with DSB vs 12 tanks with Regular sandbeds. Two tanks DSB no treatment, Two tanks SB no treatment,
Two tanks no sand bed treatment.
Use same water,sand etc on all tanks
Cycle the tanks, use just ammonia because it can be somewhat standard.
After cycle add excess phosphate to the treatment tanks for 5 days.
Do 5 80 percent water changes to remove added phosphate in water.
Test phosphate level after two weeks in all tanks.
Change water and test in another two weeks ... Repeat
Collect all data and run stats.
You don't have to be a scientist to do this. The major issue is people don't want to put in the effort or money. Also this experiment is not perfectly designed so it does not prove anything, it just supports your hypothesis.
So someone could and would say for example "I use a finer sand than yours so your results don't apply.