DSB's have been debated since their introduction.
After 20 years of using them I can tell you they fail because people misunderstand them.
Micro fauna and certain strains of denitrifying bacteria come and go and affect their efficiency. Hence the replacement factor. However, nutrients also play a huge role in their performance. Phosphates and heavy metals from tap water sources are 2 of the biggest factors. That is why RO water with a TDS of 13-36 post filter is not sufficient for a reef tank. DI resins need to be used to get the TDS to 0 ppm. 2ppm being the highest allowable reading and indicating DI resins be replaced.
By controlling phosphate concentrations, reducing the introduction of heavy metals, using a mix of adsorption materials from Activated carbon to other resins, and incorporating caulerpa in the DSB sump, I have maintained them for as long as 12 years without problem before having to move the system.
DSB's are a source of ammonium at the surface and this should be assimilated by caulerpa to avoid issues with phosphates/cyano bacteria/ dinoflagellates. That is why caulerpa grows so well near the sand bed if it is used in the main tank or fuge.
Many people who chime in on these issues have read opinions and drawn their own without evidence/experience. I have followed Dr. Ron, Dr. Bob Goemans, Julian Sprung, and others on this issue. They all have valid points that come to different conclusions. I believe in my experiences that remote 40g breeder tanks with plenums work better than DSB's, however DSB's are more practical to install with less DIY issues of fabricating the plenum. Therefore I use the DSB in a sump and only keep 2" of sand in the main tanks.
Going deeper than 2" in the main tank may lead to problems if the rockwork is not platformed and sits directly on top of the bed. I've seen plenty of tanks 2-3 years old have large pockets of hydrogen sulphide/black sand under the rock work.
Having creatures that burrow in the bed are definitely beneficial for avoiding this. I always place the rock work on the bottom of the glass and then pour the sand in around it. Less chance of burrowing to cause a rock to shift position and slide the upper rocks into the glass causing the tank to bust. I have seen this with inverts that displace a lot of sand.
Here is a link to some more on this debate...
http://www.reeffrontiers.com/forums/showthread.php?t=25455
Read all three pages.
After 20 years of using them I can tell you they fail because people misunderstand them.
Micro fauna and certain strains of denitrifying bacteria come and go and affect their efficiency. Hence the replacement factor. However, nutrients also play a huge role in their performance. Phosphates and heavy metals from tap water sources are 2 of the biggest factors. That is why RO water with a TDS of 13-36 post filter is not sufficient for a reef tank. DI resins need to be used to get the TDS to 0 ppm. 2ppm being the highest allowable reading and indicating DI resins be replaced.
By controlling phosphate concentrations, reducing the introduction of heavy metals, using a mix of adsorption materials from Activated carbon to other resins, and incorporating caulerpa in the DSB sump, I have maintained them for as long as 12 years without problem before having to move the system.
DSB's are a source of ammonium at the surface and this should be assimilated by caulerpa to avoid issues with phosphates/cyano bacteria/ dinoflagellates. That is why caulerpa grows so well near the sand bed if it is used in the main tank or fuge.
Many people who chime in on these issues have read opinions and drawn their own without evidence/experience. I have followed Dr. Ron, Dr. Bob Goemans, Julian Sprung, and others on this issue. They all have valid points that come to different conclusions. I believe in my experiences that remote 40g breeder tanks with plenums work better than DSB's, however DSB's are more practical to install with less DIY issues of fabricating the plenum. Therefore I use the DSB in a sump and only keep 2" of sand in the main tanks.
Going deeper than 2" in the main tank may lead to problems if the rockwork is not platformed and sits directly on top of the bed. I've seen plenty of tanks 2-3 years old have large pockets of hydrogen sulphide/black sand under the rock work.
Having creatures that burrow in the bed are definitely beneficial for avoiding this. I always place the rock work on the bottom of the glass and then pour the sand in around it. Less chance of burrowing to cause a rock to shift position and slide the upper rocks into the glass causing the tank to bust. I have seen this with inverts that displace a lot of sand.
Here is a link to some more on this debate...
http://www.reeffrontiers.com/forums/showthread.php?t=25455
Read all three pages.
