Oh-No here we go with the DSB questions again.

[cdemeritt]

Ok, here are some questions that may have already been discussed at lenght. I tried searching for info already on the site, but with 1437 threads to search, and most only having a someone using a phrase or two and the main thread having nothing to do with a DSB, I got lost after only a pages worth of reading. If you know of a thread, please let me know.

Ok, first, I originally was under the impression that there were many benefits to having a DSB beyond Denitrification. They are listed in very vague manners, and some are just implausable (like no more need for calcium additives). IYE what noticable benifits were there? This of course is before it becomes the Phosphate monster.

2. How long before the DBS became full? from what I have heard it is about 1 year, True?

3. When the DSB started to get full, was the change sudden or slow? Say was all good and withing a week or two started to change or did they start to have problems after only a few months and just got worse?

4. Are any of the bacteria that live in sand beds affected by light? My sand bed is in a 10g tank, and has two light zones, a small 13w 10k/atintic compact florescent light on one side, a 42w standard compact florescent on the other. The side with the 42w light has lots of the N2 air bubbles in the sand, with the area just under the light looking like swiss cheese. this slowly decreases to almost none under the 10k light. there is a small shaded area under a rock shelf, that has more than the 10k light area, less then the 42w area. Any thoughts on why?

5. The LFS recommended that the light over the DSB should be left on 24/7. what's your thoughts?


Thanks in advance,
Chris

[icebear]

there was a really good thread in the THINK TANK that gave me a migrane. Did you happen across that one?

[cath]

Yep, Chris...Heather is right. And I need to go read it too

[tdwyatt]

Originally posted by cdemeritt
...I originally was under the impression that there were many benefits to having a DSB beyond Denitrification.

There are benefits from using the DSB's, although depending on your husbandry, they may be quickly overshadowed by issues with excess nutrients that become sinked in the sandbed, in particular, phosphate in systems with heavy feeding. Some benefits include:

• denitrification (as you've already listed)
• sinking of phosphate (agreeably this is a double edged sword, systems that have export mechanisms and low introduction of phosphates may be able to extend the life of the sandbed for many many years without issues of sulfate reduction patches and excessive anaerobic beds.)
• homes for sandbed creatures
• homes for some types of fishes and eels
• organic carbon processing
• provision of some suspended organic items for corals to feed upon (mostly occasional gamete production and the release of pelagic fry, etc. of benthic worms, crustaceans, etc.)
• some buffer capacity and some ca production, but really not significant once biofilms are formed over the sand granules. Areas of deep sand anoxic beds DO become acidic enough to provide enough acidity to dissolve the aragonite or calcite sands to some extent, but by the time this interstitial high-calcium high alkalinity water percolates to the surface of the sandbed, the pH rises enough to bring the levels back to near the water column of normal seawater, insignificant in systems with decent coralline and/or coral colony pops.
• natural appearance of the bottom

There are a few others as well, but some of these are debatable as to whether they occur in closed systems or are limited to oceanic conditions.

Originally posted by cdemeritt
... 2. How long before the DSB becomes full? from what I have heard it is about 1 year, True?

MUCH much much debate on this issue, probably the main point of contention for the limits of DSB's. They DO NOT make excess carbon disappear, they DO NOT make all the detritus become nonexistent, they DO NOT make fish poop some magic disappearing residue that has no impact on the tank, although the fish poop issue is HIGHLY OVERSTATED in terms of toxicities to the tank. It does account for a gradual accumulation of heavy metals and other potentially toxic substances slowly over time, as after every pass through the gut of some lower part of the food chain there is less carbon/nutrient remaining (converted to biomass), but if these organisms die, these nutrients are re-released back into the water column. There is an argument (mostly true) that these substances are recycled, but we are splitting (sea)hares here... . The main issue involves sinking of phosphate in the sandbed to carbonate sediments and the live rock. All carbonate substrates in the watercolumn can become targets for phosphate adsorption from the water column. The biggest issue with DSB's is the INCREDIBLE amount of surface area available for this adsorption. At any given time, aproximately 20% to 30% of the inorganic phosphate in the water column may be adsorbed to the surface of the carbonate sediments. Biological activity in the SB may release some of this back into the water column, but kinetics of the water column are such that at the pH of marine aquaria drives almost immediate replacement of the adsorbed materials that were released. This does not take into account issues with conversion of organic materials (nucleotides, phospholipids, misc. proteins) into inorganic phosphates as they decompose. The contribution of these substances will be a function of the rate of their introduction into the system as a result of feeding, specimen death, top off water, etc.

Originally posted by cdemeritt
... 3. When the DSB started to get full, (is) the change sudden or slow? Say was all good and within a week or two started to change or did they start to have problems after only a few months and just got worse?

it is a gradual thing, some heavily fed systems see issues within the first year, other systems that have had export mechanisms in place and have had good husbandry in terms of detritus removal from the rock, etc. and light feeding and good SB surface area not occluded by rock may not see symptoms for many years. There is an issue of whether or not aquarists can keep feeding low enough and introduce the proper organisms that can convert the phosphates to biomass that escape management via export. This is a big issue in the overall picture, as no matter what mechanisms you have in place, the bacteria end up processing at least some portion of available nutrients available to them, and they either become the end detritus (as there are few if any organisms that cruise the sand bed depths to consume their dead carcasses) or produce end detritus waste that is unavailable to other organisms for further processing in the DSB's . Although it is difficult to maintain a functioning DSB with less than 2 inches of substrate (pretty much the factor that limits access by the benthos is the same factor that drives denitrification), shallow substrates may avoid many issues and still provide many of the benefits of the DSB (heh, forget denitrification in shallow sand beds). In DSB with little maturity and insufficient bacterial pops, black areas of sulfate reduction may develop, as well as problem areas of high mineralization of ammonia to nitrate without sufficient denitrification to reduce overall nitrate levels in the system. This may result in substrate blooms of Cyanobacteria and/or diatoms and/or dinoflagellates and/or microalgae. This may become nonexistent for a number of years as the populations mature, but then slowly begin to reappear as the sandbed becomes saturated with sinked phosphates (at that point, it is no longer bloom due to high nitrates, but phosphate will become the limiting factor in bloom control). Export of this phosphate by siphoning would be indicated, as it will them be a means of reducing overall phosphate as well as the ugly algal mat.

Originally posted by cdemeritt
...4. Are any of the bacteria that live in sand beds affected by light? The side with the 42w light has lots of the N2 air bubbles in the sand... ...slowly decreases to almost none under the 10k light...

The top 3 cm of the sand in most aquaria is an area of huge primary production by algal organisms, including Cyanobacteria (non-bloom) as well as many spp. of true algae as well. The redder the light, and the stronger the bulb, the more likely that algae will photosynthesize and make oxygen due to photosynthesis, rather than bacteria making nitrogen due to denitrification. There is little denitrification that occurs in the aerobic and mildly anoxic layers of the upper sand bed. Most of the nitrogen gas is produced in the lower third and fourth inches of the DSB and down by non-photosynthetic bacteria.

Originally posted by cdemeritt
...5. The LFS recommended that the light over the DSB should be left on 24/7. what's your thoughts?

Personally I like this, in particular with NON-CAULERPA macroalgae in systems where there are many fish and heavy feeding. Not only does it provide for 24/7 uptake of phosphates, but it also prevents the diurnal swing in pH due to the start of periods of respiration only in plants during lightless hours. This means that plants stop removing CO2 and become net producers of CO2 during the night. The increase in CO2 levels then drive pH down, until the photoperiod starts again and the plants then start up their photosynthetic machinery. During hours of light, the algae (coralline and macro) and photosynthetic symbionts become net consumers of CO2, driving pH back up as the CO2 is removed from the water column.

Sorry to make this such a long post, I hope this clarifies the issues a bit. I concur with the folks that suggest an in-depth read of the think tank threads, as much of what has been posted here is covered in detail there.

With that said, I might add that I have had DSBs since the early 90's, and their use has allowed me to keep many organisms that were nearly impossible to have thrive prior to the use of DSB's (OK, better lighting helped a bit, as well as improvements in husbandry ) I see system stability that only improves with time, especially if the tank is well-tended, limiting imports by every mechanism available and pushing exports whenever possible including frequent water changes.

end of part one, TRT says the response is too long, part two to follow this posting

[tdwyatt]

part 2

I personally get a lot of email from folks asking about all the noise about DSB's in general. I am slowly getting information together about the issues that seem to plague those aquaria that have DSB issues or outright failures. The following is a cut and paste from one of these emails:

from a personal communication w/ tdwyatt:

I am not really sure that I can speak with true authority on this, as I am still collecting data and see an occasioinal blip in the data that does not support the overall concept I am seeing, but for the most part, suspending the rock on pilings above the sand does appear to prevent many of the problems reported to be associated with DSB's.

The following are things that seem to be showing up as common reasons for failure:

• less than 2 to 3 inches sand
• heavy feeding of either the sand bed alone or heavy fish pops requiring heavy feeding
• low coral populatioin densities (don't ask me on this one, I am clueless on this although I have some thoughts)
• skimmerless systems with no apparent export for nitrate nor phosphate
• greater than 1.5 lb/gal density LR and the rock directly on the sand (go figure on the amount/gal, might have to do with detriutus shedding)
• infrequent or non-existant water changes

These seem to be the areas of contention, a few other issues as well related to low intensity lighting, lack of detritus management, poor current management at the substrate level, but the numbers are non conclusive, as well as indications that alkalinity may play a factor as well

There are very definitely limits to what we can expect from DSB's, some limits are imposed by the rate at which we operate and feed (think phosphates), some limits are imposed by the organisms we decide to keep, other limits are restrictions due to time, timing, and how long we can expect to avoid the laws of chemistry and physics. Some limits are manageable, some are controllable, some are incontrovertible, but they all exist nonetheless. The trick is finding a happy medium within which we can operate, realizing that these limits do exits, and DSB's require careful tending and maintenance. They are not the carefree "set-it-and-forget-it" mechanisms we have been lead to believe.

hth

[Jayhawk88]

Ticking the "search titles only" option will refine your search quite a bit. Hope that helps. I don't know too much about DSBs other than they sound like more trouble to me than they are worth.

[ruhspolostar]

sound would be the key word wouldnt it

[Nafe]

Im more inclined to follow toms example rather then listen to many uneducated and in-experienced reefers opinions on DSB's. Often the experiences they qoute could have been avoided by better management.

Rather then write off DSB's perhaps we should be trying to emulate Toms systems, obviously he is doing it the right way, or at least a far better way then others.

You can expect lots of questions from me soon TOM as i set my tank up

[Spanky]

Originally posted by Nafe
Im more inclined to follow toms example rather then listen to many uneducated and in-experienced reefers opinions on DSB's. Often the experiences they qoute could have been avoided by better management.

I'm sure you didn't mean for that to come across so snooty.

[cdemeritt]

Tdwyatt

Thank you for the info. I feel fortunate that I set up the DSB in a refugium, so as to make it easier to maintain. Most of the items on the list of failures won't be a problem as I do skim, Don't feed much, change water frequently, have a frequently changed floss pre-filter, low animal pop., high macroalgea pop. have a LR to G ratio of about 1 to 1. and good flow.
I wrote a very large and detailed message a few minutes ago discribing my tank setup, and managed to delete it before hitting the submit button.
I do have one question, you wrote "Personally I like this, in particular with NON-CAULERPA macroalgae in systems in responce to my 24/7 lighting question. Why is this? I currently have C.racemosa, C.Taxifola, As well as a Sargassum sp. , chealomorpha, and 2 types of halimeda. and hope to be adding some more brown and red types.
Thanks again,
Chris

[Nafe]

Originally posted by Spanky
I'm sure you didn't mean for that to come across so snooty.

Sorry didnt mean it to come across as snobby...however it was meant to be pretty straight forward. Simple fact is too many people dont manage there DSB's correctly, and then come onto the forums proclaiming the problems they had with DSB's.

I just think we should stop degrading them, and have a look at the way TOM manages his aquariums with great success and see if we can follow suit. I feel that if we did there would be far greater success with DSB's and i intend to follow his lead as close as possible with my new tank.

[Spanky]

So that's a fact huh?

And I just think you need to read these two threads and tell me how many "new" "inexperienced" people didn't manage their DSB's correctly. ROTFL

http://reefcentral.com/forums/showth...hreadid=263482

http://reefcentral.com/forums/showth...hreadid=210605

[Nafe]

Umm yes it is a fact, there are so many examples out there it isnt funny.

Spanky im not saying all people who have had problems with DSB's are new and inexperienced, however a great deal of them are. I consider a year or two still very inexperienced reef wise. I include myself in the inexperienced region.

You know just because some people are seasoned reef keepers it doesnt mean they are doing it the right way. Obviously tom is doing something right with his DSB's, they are outlasting other systems by a large margin, and i am led to believe that most havnt even got to a stage of saturation even after years and years.

Perhaps we should listen to him and emulate his systems?

[tdwyatt]

Thanks for the vote of confidence Nafe, but I am not sure that for maximum stability that bare bottom systems may not be the best long term solution. Using sand DOES make for stable safe systems, it's just too bad that the term is limited. So far, I have found 4 other persons that are using DSB's and have more than 5 years of success, using pretty much the same husbandry attitude that I use. I think that such systems are the most beautiful, and with such an opinion (there are plenty that don't like the look of DSB's), DSB's are prolly the way to go, as they do not require the constant sediment vacuuming, etc., that bare bottom tanks or shallow sand beds require.

If you want sand in the tank, and you don't mind thinking about doing a partial change of substrate in stages at 3 to 5 years down the road, then DSB is definitely more stable and has a safety net in terms of the water column nutrient issues. To me, the issue of changing the substrate in a few years down the road is much easier than doing once-every-2-to-3-week bottom cleanings (heck, I am so lazy that I have a tough time making myself do once a month turkey blasting the rock for detritus). AND, you better have some means of backing up your power for the pumps in case the power kicks out, as the DSB's are high oxygen users in the absence of light and current, dropping the O2 level to the 2 to 3 range in a 180 gal tank in less than 24 hours under these conditions. I did the math on the rate of the oxygen consumption in a powerless tank based on sediment pops of 1 x 10^9 colonies per g substrate and standard diffusion rates for 12 sq. ft of surface (180 gal tank) and 2 ft depth at 80F. Depending on who's studies and the proximity of stands of stony corals, respirations in mg O2/gram substrate per day varied from 0.13-0.26 in coral sands close to large coral pops to 0.21-0.23 for coral sand and rubble to 2.4 to 12.0 in detrital sediments near low pop density coral stands (ouch!). A few studies dropped consumption rates to as low as 0.05, but much of this is dependent on current, proximity to terrestrial pollution, and river and clay sediments. Areas like the Florida Bay prolly don't have a chance with all the phosphate that is pumped into the bay from land based operations (too many people live in S. Florida for such close proximity to coral reefs).

OK, I got off track, my biggest concern for DSB's is potential loss of power, inadequate oxygenation (may be rock placement, may be poor planning), and heavy feeding that leads to the issues that seem to promote rapid DSB failure. You'll need to follow good husbandry, good exports, and think corals, not fishes.

Oh, and you'll prolly need to get a pair of asbestos underwear, as many folks will give you a TON of grief about using a DSB, esp on Rookie Central... Me? I just keep plugging along, enjoying the corals, the few fish I keep, and the sand bed critters I enjoy.

Thanks again for the vote of confidence, hope this helps.

[Nafe]

Tom can you give an example of the fish you keep, amount, size, tank size etc.

The tank i have is 48" long 20"high and 20" wide. With a 4 inch DSB and filtration provided by the live sand/Rock resting on pvc. What would be an maximum fish/invert load you would recommend from your experience.