Back on track: DSB's work well due to their bacterial function This is both their strength and their downfall. DSB's work partially due to the many things that have been listed in the 10 commandments, as they DO process Carbon, the DO break it down to its final mineral ash, bacteria do play their role in doing the nitrates and they DO sink a goodly amount of the stuff we don't want in the water column. Heavy feeding will always load the water column with nitrogen, phosphates, DOM as fats, carbohydrates and proteins, and minute particulate materials (forgive me, but for the sake of discussion, reef AQUARIUM snow and I don't mean 2 little fishes product
). In addition, much of this material plays a role in the primary production of the first 2 or 3 cm of the fine sand beds, and actually, is improved in terms of both rate and total volume by the finer sand and the sediments that are actually silts (don't make me show you the math!). Production and consumption is cycled on a daily basis by the trophic bacteria in the substrate
and anything else capable of grabbing a piece of the nutrient pie.
We want these things that get the most of these organics to be larger organisms: macroalgae, microalgae (in the case of those that are fed on by snails), sea cukes and misc. nematodes, polycheates, etc. that are either capable of being consumed by higher organisms and turned into biomass, or are harvestable and exportable, which is what making the DSB work is all about: making the stuff we don't want exportable.
The following things don't really work by themselves:
- The sand bed, no matter how deep it is or how well it is tended.
- macroalgal refugiums
- algal scrubbers
- skimming
- carbon filtration
- ozone treatments (I hope none of you are using this still)
- UV treatments
- water changes
- estuary tidepool remote ecosystems
- shallow sand beds with cleaning
- settling tanks with siphoned removal of detritus
Each of these things by themselves have limits or disadvantages to the way the work to limit the amount of accumulating organics and end detritus. Either they miss a portion of the materials they are intended to remove or they require massive and consistent maintenance to function or their efficient function may cause detrimental effects to the overall operation of the system we want to run.
The trick is to find the right combination of these means of controlling nutrients/organics/end detritus that works well in view of the already demanding schedule of maintenance for our little biomes and will accomplish our end results with as little interference from us as possible (i.e., keep yer hands out of the tank...). Sure we can do it without a sandbed, if you enjoy spending your time pooperscooping your fish...
I guess it all goes back to what do you want to see in your aquarium, and how do you want to approach it.
Horge has made several posts in this forum regarding the success of bottom up vs. top down controls for algae/nutrients. How do you make sure that you have the right creatures for top down consumption and sequestering of the nutrients?
Which creatures will graze the sandbed effectively to eat the bacteria algae off the sands? How do we assure that the microalgae will be consumed and converted into biomass (snail meat) ? What can we (the ultimate top consumer) do to either limit the inputs or better export these unwanted substances? This is a part of what we want to know, but we still have to find a means of performing these functions and still contribute to the overall health of the corals.
DR Shimek's comments have always alluded to the need to feed our sandbeds, and in part this may be true, but heavy inputs still leave behind heavy leftovers, end-detritus does not export itself. To control the rate at which our DSB's fill up, we have to either:
- [a]find a means of limiting the total inputs
limit the access of bacteria to these substances
[c]compete for the nutrients aggressively
[d]find organisms that will consume those bacteria that do sink end-detritus (converting those substances to biomass)
In addition to the bacterial end consumers (that are either too deep in the sandbed for consumption or fluxing conditions in the sand bed prevent their consumption) we still have abiotic processes that account for sinking of many undesirable substances in the sand bed. There are a large number of heavy metals that chemically bind or are in ionic association with carbonate sediments. All the divalent ions are capable of binding in the place of calcium to the carbonate in the sand bed, some form insoluble bonds, some are in equilibrium with soluble phases of the ionic forms. Phosphate is a good example: It forms a highly insoluble salt with calcium and precipitates out of solution, especially with Kalk additions, effectively removing phosphate as a source for nuisance algal blooms. The sandbed has no export or processing capacity for phosphate, so this substance builds over time, leading to potential mass release during substrate disturbances (like stirring the substrate). The only way of preventing a buildup of phosphate is to find some way of exporting it, either (can't believe I'm saying this) use an algal scrubber and harvest the microalgae, or use a refugium (my preference) and export the macroalgae.
We still want some of the foods that come from the DSB, although they are incapable of producing significant planktonic foods at levels that will truly help us. Refugiums with macro- and microalgae can produce some, but the numbers we need in a sump or refugium the size most of us are keeping will not do the trick, no matter how much we feed it or even with 24/7 lighting. By itself, these are really just another excuse for most of us to buy another set of lights and more sand and detrivore kits, yadda, yadda, yadda (don't let my wife see this! ;D ). Based on the trophic and primary production of natural reefs (and we can't come even close), we would need approx. 3 sq. meters of appropriately selected organisms to be able to provide the plankton for feeding of 1 moderately (by aquarium standards) sized coral. (I will document this if you want, but don't push me, I'll get Chris to write a supporting article to the article I well get Spanks to write... ) I keep thinking back to the issues we see with Gonoporia, Alveopora and Heliofungia spp. and dirty biotopes supplying massive nutrients, I can't help but think that their demise in captive reef systems still goes back to inadequate nutritiion (sorry for the aside)
Soooo.... after this tirade, what does that leave us with besides squinty eyes and headaches? Finding means that work t control inputs, harvest exports, and somehow biologically pull out of the sandbed the things that become trapped in the biological (bacteria) filtration of the sandbed. It will definitely take every means at our disposal to accomplish this, but even then, the bacteria will ultimately trap a great deal of the little things that "slip through the crakes" in our best efforts to prevent supplying nutrition down to the bacterial level.
This is what will make a DSB work, albeit for a limited time.
DSB's do work, They work well when constructed correctly, established over time, and tended carefully. The trick is still in the details of out husbandry skills. We will need to watch them as we would a bathtub with a leaky faucet dripping into it, and we can't remove the plug. Much like this tub analogy, we can control how much stuff goes in, and we can bail water out over time to prevent it from overflowing (even to the point where we could take out some of the sand), but that is where we stand at this time. The sandbeds have limits, and although we can make them work and work well, there will come a time where they will need drastic measures to keep their functionality.
OK, it is thundering outside now, so I'll stop my tirade (before the power blinks and I lose this post), I have a lot of other thoughts on all of this, but much if it is experience-based and not documented. I have seen too many systems that operate without flaw, but will require maintenance nonetheless. I think the knee-jerk response amongst many will make the DSBs become what skimmerless systems have been for a while, another craze that comes and goes.
