View Full Version : DSB Particle Size

07/20/2007, 04:07 PM
I've read probably 25-30 articles on the use of DSB in reef tanks.

What I don't understand is WHY can I not use crushed coral as a DSB?

Please explain that to me.

If I already have 30 pounds of crushed coral in a 30 gallon tank--can I add fine particulate sand on top of that cruished gravel?

Taking all the gravel out is really not an option. Can the sand and gravel be mixed?

Could I move all the gravel off to one side of the tank and pour the sand in on the other side?

Can I layer the sand right on top of the gravel?

Can I layer the gravel on top of the sand?

If you recommend adding sand to the existing gravel--how much sand can I add? 20 pounds? 40 pounds? 4"? 6"?

If there is just absolutely no way of incorporating the gravel and sand together, what can a guy do with 30 pounds of crushed coral?


07/20/2007, 04:21 PM
The large particle sizes of crushed coral have two disadvantages:

1) Surface area. As a particle gets smaller in size, the ratio of surface area to volume goes way up. So, for a given volume, larger particles will have much less surface area. Less surface area means less real estate for bacteria to colonize.

2) Porosity. the larger particles of crushed coral will have way too much empty space between them in a bed. This will allow water to flow through the bed far too easily, meaning that you'd need a much deeper bed to get to the point where mixing has reduced enough that the bottom has become low enough in oxygen to support anaerobic bacteria.

You can't layer the substrates without something between them to divide them (which would ruin the whole concept), they'll just mix together over time. You could mix the sand into the gravel, but then you'd still be facing point #1 above for a certain portion of your bed.

What to do with 30 lbs of crushed coral? Lotsa things. Make home made rock with it. Use it as media in a calcium reactor. Sell it to unsuspecting friends!

07/20/2007, 04:29 PM
I use crushed coral for my DSB, but the particle size is more fine than the gravel type that some use to cover the bottom of their fish tank. The larger the particle size the deeper the DSB has to be to facilitate the growth of anaerobic bacteria. So when most say that crushed coral can't be used it is because the larger size would make it hard to have a DSB, unless it was very deep. Most people have done away with using DSB's in their tank and swtiched to using them in their refugiums. This is seems to be a result of the consequences of having the DSB disturbed in the tank which often causes the entire tank to crash. Refugiums don't usually contain anything that would disturb the DSB and the risk of having a tank crash because the DSB was disturbed is reduced. DSB's also need to be regenerated after they have been in use for a while, generally a couple years of use. This is due to the fact that DSB's are not disturbed and fine particles will eventually move in between the sand particles which will stop the water above from slowly finding its way to the anaerobic bacteria. So, to avoid any problems a portion of the DSB is removed and cleaned to remove the fine particles that have built up. It is then replaced and later a different portion is removed to be cleaned. This allows the DSB to function continuously without any major disruptions to the nitrate reduction potential of the DSB. I would really recommend that you use a single, consistent substrate with a particle size of around 1.0-1.7mm, this seems to be fairly standard and has had good results. A depth of 4"-6" is usually used with this particle size for a DSB. This would allow you to keep the more coarse sand in the tank while using the more fine sand for your remote DSB.

Here are some interesting threads if you want to do some more research. Anthony Calfo's thread on remote DSB's is a good read, his use of a 5 gallon bucket for a DSB is pretty cost effective and seems to be very helpful in reducing nitrates. Here is the start of that thread, its pretty long but well worth the time.


07/20/2007, 04:35 PM

07/20/2007, 06:13 PM
<a href=showthread.php?s=&postid=10381349#post10381349 target=_blank>Originally posted</a> by TurboSnail8898


I think I gotta tear my tank apart and go to Home Depot. :eek2:

I made it to page 8 before my eyes got tired. I'll read the whole thing eventually. Really appreciate the link to that. Interesting reading if you can manage to skim past the bickering.

What is the final concensus on CPW in the DSB? That thread was started back in January 2004. Thats been 3.6 yrs ago. Are people still doing it?

07/20/2007, 08:33 PM
Remote DSB's are used by many reefers, especially those who keep SPS coral and are worried about nitrates (SPS are very sensitive to nitrates).