DSB question

[Leandre]

afternoon,

so...ive decided to to make a chaetomorpha reactor with this large SSA media reactor i have. it was way bigger then i needed. so i bought a med size reactor for carbon/gfo and planing to make it.

article about the cheato reactor: https://reefbuilders.com/2016/08/31/...orpha-reactor/

now, back to post. i now have an empty space in the external refugium and i was thinking on a deep sand bed.

a little info:
the refuge is a 40g breeder thats been sectioned off into two parts. the small part measures 9"x18"x14"t. the large section i have about 40lbs of large left over rock. the water flow comes from the manifold from the main sump so it been through filter socks. the flow rate through this refuge is small, maybe 30gph? the DT is a 220g (total water volume 250-260) has been up a little over a month now. cycled and had a 2" sandbed 4 beginner corals, 1 fire shrimp and 2 cleaner shrimps. 30 trochus nails and 30 hermits. also has like 12 chermois in it. i found the fire shrimp molted some time last night. ive had him a little over a week, so i must be doing something right. crapped myself this morning when i saw pieces of shrimp floating around.

now my question is, should i use that small space for a DSB? if so what sand is best? ive read "as fine as you can get" also, live or dead? can i use play sand? do i need to add snails and such?
detritus will be minimal in this area. the main goal for this is to cultivate more anaerobic bacteria and a place to grow pods. would setting up a DSB now upset what i have already?

what are your thoughts on this?

 

[DaveK]

I would forget about a DSB in an area that is only 9x18. BTW, this also applies to some of thses very small hang on the tank refugiums.

The main purpose of a DSB is to do denitrification. You need a fairly big area for this, because this process happens a lot slower that the typical nitrification process.

As for the granular size of the sand used, for pod production you want it course. For denitrification you want it fine. If your trying to do both, choose something in the middle.

Lastly, just because this space is empty it doesn't mean you need to fill it up with something. Feel free to just leave it empty, unless what your are doing to do will make a major improvement in the tank.

 

[Leandre]

At 9x18x14 can fit about 40lbs of sand. That's too little?
I mainly want to use it to grow pods, denitrification is a bonus, so most likely use something like Fiji pink?

I have no problem leaving it empty. Just I really want manderines. So thought why not...

 

[DaveK]

Yea, you can put 40 lbs of sand, but pod production only occurs in the top couple of inches. Going deeper than about 4 to 6 inches can be done for denitrification but it's not going to be that much better than 4 inches deep.

Ideally you want just a little circulation through the sandbed for denitrification. That's why most denitrification filters run water through them in so many drops per minute. In a really deep sandbed you get almost no circulation.

 

[Leandre]

Ok, so 6-8 inches is the norm. Having 6-8 in the space is kinda pointless. What if I used the whole 40g breeder space 36x18 and had it 6-8" high and the rocks sitting on top of the sand with low flow. Would that be better?

 

[DaveK]

Here is the thing about an 8 inch DSBs in the main tank. The deeper you make the sandbed the less water will be in the tank. This means that on a 40 gal breeder tank you loose almost 50% of your water. Even a 4 inch deep sandbed will reduce the water volume about 25%

So you got to ask yourself, is the reduction in water volume worth the advantages of a DSB? A lot of this comes down to what you want to keep in the tank.

Sandbeds are something where you usually can't go too far wrong. After all you see great systems using no sandbed, a shallow sandbed or a deep sandbed.

 

[Leandre]

My tank is a 220g with a 40g sump and an external 40g refuge. Total water volume is like 260g. The DT has a 2" sand bed. The space I'm taking about is the 40g refuge. Initially I split that tank into two sections 2/3 with left over rock. And 1/3 (18x9x14t, the baffle is 14"t) I seperated it so cleaning would be easier. At this moment I wanted to make a cheato reactor with a large sea side aquatics reactor I have already have. The space I'm talking about is in the 40g external refuge.