DSB Heresy

[salty joe]

It seems no matter what, unless their was a constant draining, water transfer between the DSB & tank water is inevitable.

Tell me if I have this right. The regular draining of the bottom of the DSB is intended to prevent the DSB from becoming saturated with toxins, while maintaining bacteria, including nitrate eaters.

Idrhawke, what is the nitrate level in your tank & how long have you used CPW? How heavily do you feed your tank?

 

[ldrhawke]

It seems no matter what, unless their was a constant draining, water transfer between the DSB & tank water is inevitable.

Tell me if I have this right. The regular draining of the bottom of the DSB is intended to prevent the DSB from becoming saturated with toxins, while maintaining bacteria, including nitrate eaters.

Idrhawke, what is the nitrate level in your tank & how long have you used CPW? How heavily do you feed your tank?

Just checked......NO3 just barely dectectable. NO3 hasn't shown on the scale since I started using CPW and never shows up even when I feed heavy. My probelm has been phosphates.

I feed heavy ( 2) frozen cubes plus dry food per day.

I have way too many fish for the 45g tank and 15 g fuge system size.

A large Yellow Tang, (3) Clowns, (2) Mandrins, (a breeding pair of Bangga Cardinals, Yellow Watchman, Algae Blenny, Yellowheaded Jawfish, and a large Copperband that I just got to eat all the aiptasia that have started to grow.

Very little algae now that I have phosphates down. A little hair algae the grows on the top of my liverock column where it breaks the water surface and collects any food before going over the overflow.

The coral ranges from leathers, zoos, mushrooms, pagoda, frogspawn, to SPS frags Montipora, Hydnophoa, acropora.

The SPS are just starting to show good growth since I have gotten phosphates under control and down.

The system is going on 10 months old and about 5 with CPW. CPW isn't hurting my efforts.

Last week I removed my (4) 75 W VHO's and replaced them with another 250w MH for the SPS.

I am now attempting to improve further improve upon CPW with tuning rates and frequency, and I am also looking at another modification to hopefully allow it to have a more positive affect on helping to reduce phosphates further and still process nitrates...time will tell.

 

[voodoody]

Idrhawke,

I am in the process of designing a 240 gallon reef tank and want to give your CPW concept a try. What modifications would you make to your current system with what you currently know? Can the plenum drain directly through a bulkhead on the tank bottom? Thanks in advance.

 

[javajaws]

"I was wondering what your opinion on this matter was, considering that you are throwing away any water that has been treated by the DSB. DSBs denitrify the water by allowing a very slow flow of water to low oxygen zones where anoxic bacteria use nitrate as food."

Excuse me for butting in here, but what EXACTLY is the problem with throwing away water that has been treated by the DSB? Nitrates go into the DSB, DSB breaks down the nitrates, broken down nitrates (??) get flushed down the drain. Successfull nutrient export. What's the problem with that?

It may not be as efficient as being able to flush everything out of the system via skimmate, etc...but who cares? The man wants a sand bed for whatever reason...and this seems a viable approach to deal with having one.

 

[javajaws]

"The view I have on CPW at the moment is that, all it achieves is the processing of tank water before it gets thrown away. Why bother processing the water with a DSB if it will get thrown out anyway?

Think of CPW (in concept) as a skimmer that uses bacteria instead of bubbles. The skimmate/(sludge?) you remove is not like removing normal tank water. The skimmer/DSB gathers the skimmate/sludge for you so that the garbage in it is more concentrated than the garbage content of the tank water in general.

 

[DennisRB]

The point is, treating water that is to be thrown away is pointless. If CPW is used in such a way that it significantly limits water transfer between the DSB and tank water. The DSB becomes redundant since the only water the DSB effects will be dumped. The idea of a DSB is that water very slowly flows in, it becomes denitrified, then slowly flows out into the tank water.

Does everyone agree that is what a normal DSB does?

"Think of CPW (in concept) as a skimmer that uses bacteria instead of bubbles. The skimmate/(sludge?) you remove is not like removing normal tank water. The skimmer/DSB gathers the skimmate/sludge for you so that the garbage in it is more concentrated than the garbage content of the tank water in general."

A skimmer lets the water pass through it, it treats the water, and then the treated water goes back into the tank. Not the sink That is if CPW inhibits water transfer (which is really the question)

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Lets look the transfer points of a skimmer for a second.

Dirty water in, clean water out, concentrated waste out. Water goes in and out via an inlet and outlet pipe. The waste is removed by bubbles at the top and discarded.
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Lets look at the transfer points of CPW DSB in a skimmer like way. (I also assumed that CPW is supposed to work in a skimmer like fashion going by the Doc's posts)

Dirty water goes in the surface of the sand bed, the DSB treats it, the clean water goes back into the tank, crud is drawn off the bottom of the DSB.
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Fine. But how can it physically do that? How can dirty tank water flow in the surface of the sand bed and clean water flow out?

This assumes that bacteria in the DSB somehow grabs pollutants and directs them down while sending the clean water up at the same time. The bacteria will only send harmful stuff toward the bottom, but they will find any nitrate and convert it and send the cleansed water back up. I did not know that the bacteria had the physical ability let alone the intelligence to do this.

 

[javajaws]

Just an FYI, I am not in the pro-DSB/CPW camp. I just happen to believe that it is a viable form of nutrient export...maybe not the most efficient export mechanism, but one nonetheless...having said that:

"The point is, treating water that is to be thrown away is pointless. If CPW is used in such a way that it significantly limits water transfer between the DSB and tank water. The DSB becomes redundant since the only water the DSB effects will be dumped. The idea of a DSB is that water very slowly flows in, it becomes denitrified, then slowly flows out into the tank water.

Does everyone agree that is what a normal DSB does?"

Well, not being one who believes in DSBs, I'll disagree (just to be different). I'm sure there is some water transfer between the DSB and the tank water, but it's not as significant as the DSB advocates would like us to believe. Here's some food for thought, a quote from Randy Holmes-Farley (http://www.advancedaquarist.com/issues/august2003/chem.htm):

"When it (nitrates) is produced on the surface of media such as bioballs, it mixes into the entire water column, and then has to find its way, by diffusion, to the places where it may be reduced (inside of live rock and sand, for instance).

If it (nitrates) is produced on the surface of live rock or sand, then the local concentration of nitrate is higher there than in the first case above, and it is more likely to diffuse into the rock and sand to be reduced to N2."

What is significant is the detritus and other junk that gathers in the sand bed. In a non-DSB sand bed (1-2") this junk will sit and rot in the bottom of your tank (where it can easily be leeched back into the water). In a DSB, it will work it's way down (thru sifting, gravity, diffusion, etc.) into the anoxic zone(s) of the DSB and get broken down. In a traditional DSB, this anoxic sludge is the proverbial ticking time bomb. In a CPW system, it is systematically drained so as to not (theoretically) explode or start reverse leeching of junk back into the system.

Now, would I use a DSB or CPW in my tank? #$%@ no - it's not worth all the trouble! The only point I really am trying to make is that there is no clear right or wrong way to run a tank and in particular no definitive 1 way to remove excess nutrients in the system. I believe a DSB will work for awhile (like a sponge), and a CPW will help that sponge last longer (length TBD). And I do believe that sooner or later your sponge will probably need to be replaced.

 

[DennisRB]

Good post

So you say DSB's don't really dentrify tank water, and CPW may just remove sand bed detritus build up? Your CPW argument holds true if the only thing DSBs do is collect crud and hold it permanently. In this scenario CPW would be great for waste export. Since you say DSBs don't work well for denitrifaction, would you say that CPW has to be used with a DSB then, and it would not work with say a 2 inch bed? Because you did mention that a all a 2" sand bed does is collect waste at the bottom.

What do you say about this theory Doc?

"When it (nitrates) is produced on the surface of media such as bio balls, it mixes into the entire water column, and then has to find its way, by diffusion, to the places where it may be reduced (inside of live rock and sand, for instance).

If it (nitrates) is produced on the surface of live rock or sand, then the local concentration of nitrate is higher there than in the first case above, and it is more likely to diffuse into the rock and sand to be reduced to N2."

I'm not sure what that quote was meant to mean in this context? It looks like it came straight out of a trickle filter nitrate factory argument. I have heard it may times.

FWIW, I'm not on either camp. I am just trying to think of all possibilities by looking at various systems and picking out issues that stand out. Doing this can create more knowledge by deeper understanding for me and others too. People might say this or that is wrong with a certain argument, which it great only if they can explain the situation, that way everyone learns something. I might even use CPW on tank I am setting up ATM, I would just like to know more about it than claims of what it can supposedly do.

 

[javajaws]

"So you say DSB's don't really dentrify tank water..."

Hang on...I'm not saying DSB's don't denitrify water...just that they don't eliminate nitrates entirely in the way you indicated (flow of water through the bed).

"...would you say that CPW has to be used with a DSB then, and it would not work with say a 2 inch bed?..."

Yes...there's minimal (if any) anoxic areas in a <2" bed. If you don't have the anoxic sludge to remove, why use the CPW?....

...And this in itself is the problem with shallow sand beds...they collect detritus that is left to rot...and because they have no anoxic zones they have no way to remove those things other than manual intervention (siphoning, man-made hurricanes, removal/replacement, etc.).

The part I don't understand (yet) is if using a CPW keeps phosphates (in the form of calcium phosphate or bound to calcium carbonate) in the DSB from re-entering the water like what can happen in a sand bed (normal or deep) without CPW. To me, this is more important than the DSBs ability or non-ability to remove nitrates (that's what we've got rock and skimmers for!). My gut feeling tells me the CPW helps (but by what mechanism: biological? mechanical?), but not enough...especially over the long term. Has anybody tested the CPW sludge for phosphates (organic and/or inorganic)?

 

[ldrhawke]

I'm not sure if this file will post. This is a test.

DIDN"T WORK>>>>TOO SMALL

You can't say I'm not trying to keep everyone happy...:lol:

Can't wait until DennisRB gets some water and coral in his tank. Something about living in the real world that teaches humility.

Anyway, something else for a few to throw rocks at and debate.

Actaully, the simple version of CPW is doing a great job on nitrates, but with the amount of food I add to the tank. SPS only tanks are nice but I like fish too.

I'd like to experiment and see if I can improve on phopshate reduction through the biological bed. It may not work, but it's fun testing different ideas.

 

[ldrhawke]

see if this works..... nope

having trouble reducing file size and not physical size....

 

[ldrhawke]

Try again....

 

[javajaws]

Whoa....I guess I haven't been paying attention. I thought CPW meant controlled plenum wasting. What you describe in that image is more like controlled plenum WASHING.

 

[ldrhawke]

Just trying to keep DennisRB happy.....

 

[ninja750]

filter material

filter material

Can cotton filter material be used between the pipes and the DSB???

 

[Obi-dad]

I think cotton will decay. Walmart sells polyester felt by yard, cheap.

 

[ldrhawke]

Don't use cotton...it will be eaten by the bacteria in a month. Use a synthentic construction drain cloth. It used in construction to hold back soil and allow water to drain through. It used it applications like making a railroad tie barrier and using it as a barrier before filling dirt behind it. It is sold in most big hardware stores. It comes in 4 ft. wide rolls, much bigger rolls than you need, but it isn't real expensive. I got mine in the Garden Dept at home depot.

 

[ldrhawke]

One of the other RC members sent me a photo of his CPW plenum piping. He did a nice job. He buit it out of 3/8" cpvc. I built mine with 1/2" pvc. You can get more piping fit into the bottom with 3/8" cpvc.

 

[ldrhawke]

Photo of a CPW plenum

 

[salty joe]

That is nice work. I'm considering using 1" non perforated pipe the length of the tank for a center with a lot of perforated 1/2" pipes attached to center pipe at right angles. The drain will come off the center pipe. The idea is to have as equal as possible negative pressure on each perforation.