The term "crash" was originally used by serious
SPS keepers who also had sandbeds. It didn't mean that the tank died by a release of Hydrogen Sulphide, it referred to the point in time where the sandbed betrayed them and started putting Phosphates back into the water column. For
SPS keepers, this is bad for several reasons. One reason is that Phosphates inhibit calcification by
SPS. The other reason is that Phosphates overfeed the symbiotic dinoflagellates inside the
SPS. Since the dinoflagellates are green and yellow (brown when put together), an overabundance of Phosphates turned their nice colorful tank brown. It was called a crash because there was no way of predicting when your sandbed would turn on you, once you knew it was happening, it was too late. Your corals were already affected....I.e. "crash".
You could have the same thing occur in a softy tank and it wouldn't be considered a crash. Softies do quite well in nutrient rich environments. However, you likely won't like the looks of the tank as you are almost guaranteed substantial algaes.
Hydrogen sulphide problems are rare. The bad that the anaerobic Sulphate Reducing Bacteria's produce can be offset by anoxic Sulphide Oxidizing Bacteria. Typically, this type of crash only happens (and rarely at that) when there is a massive disturbance to the lower layers of a
DSB.
Then the terminology of "crash" got confusing. Dr. Ron started discussing sandbed crashes as a result of heavy metals. (That is utter nonsense
BTW). So now when you hear the term "crash" you really need to be clear about you mean.
Do you like the looks of sand, want to keep animals that require it, etc? If so go for it. Just understand that
DSB's do not do what a lot of people think they do. They were sold to the hobbiests was that you could put sand in the bottom, put some animals into the sand, and that the matter that goes into the sand suddenly goes "poof" and disappears. It would be nice if they worked like this but that would break several laws of science including the law of conservation of matter. Here's what sandbeds can do fairly well.....process Nitrogenous compounds. Here's what sandbeds cannot do....remove Phosphates. They are just temporarily stored in the bed in an inorganic form (adsorbed to the sand) or in organic form (inside the body of the bacterial biomass or sandstirrers). Unfortunately, over time, your sandbed fills up with mulm and other solids which raises the Anoxic level and shrinks the aerobic level of the sand. Once the anoxic level gets high enough, phosphates will start hitting the water column. If you keep
SPS, understand that you could very well have a problem down the road. Some tanks go 2 years, some tanks go 10 or more years. There are many variables involved.
I've run
DSB's, SSB's, and BB systems. There's nothing wrong with any of the systems. You just need to understand how they work. Right now, I'm watching people get sick of cyanobacteria and algaes so they're are yanking their
DSB's and going barebottom. In six months you are going to see people say, "I went BB and now I have high Nitrates". If you pull your
DSB out but fail to siphon up detritus or have your flow good enough to get the detritus out, you're going to get Nitrates. That's just the way it works.
