DSB Heresy

[ldrhawke]

Thanks jrm01!
I knew it wasnt Tom Frakes, but couldnt remember a simple name like Miller
IIRC, He had the same general opinion that the plenum goes sour and is a nutrient sink. He didnt waste nearly what ldrhawke does, though. I bet he kept his nitrate reducers happy, though.

ldrhawke,
It seems you don't mind the nitrate reducers being over run with aerobic bacteria due to the volume of your water changes. Do you expect, or have you experienced, that the nitrates will stay very low with water changes only?
Chris

Maybe you or someone else can explain something to me.....what makes people believe, even if you have some de-nitrification taking place below a couple of inches of the bed surface , that you have adequate water exchange rates between the water column above and that lower dead zone, to have any affect on reducing nitrates in the water column?

I have read theories about how the bugs and osmosis cause turn over in the bottom of a DSB, but I haven't seen any data to substantiate the theory. Can anyone produce data that proves there is an adequate rate of water turn over in the denitrification zone taking place to have any sustantial affect on the water column above. :rolleye1: I could put a capped bottle of waste in the bottom of the tank and it could produce denitrifying bacteria, but unless you have fluid being exchanged it has no affect on anything.

Or to give another example and ask a question: I could build a denitrification coil and remove the waste from CPW and feed it through the coil to denitrify. Even if I put a very small volume coil and only fed it at very low rates, it would be denitrifying. How large a denitrifying coil would you say had to be installed to keep nitrates from building up in the tank? It's physical volume and the allowable flow to maintain denitrifying bacteria will determine it how well it works or if it works at all.:eek1:

I do believe there is denitrifying bacteria, along with sulphide bacteria in the bottom of any tank substrate, but I have yet to see anything that proves there is any realistic rate of fluid exchange, between it and the water column above, to have a positive affect on the tank water.

What I have been baffled by is that alot of people blindly accept this exchange is happening, with out proof or even logic to support it. But they question CPW that is at least producing numbers and data.

Plus, as I have said before, with the CPW concept you really don't care if you have denitrification taking place or not in the substrate. The concept is to physically remove the nitrates, phosphates, and other organic waste being produced or introduced; and keeping a positive flow into and out of the bed and not allow the waste from flowing back into the water column.

 

[H20ENG]

"Can anyone produce data that proves there is an adequate rate of water turn over in the denitrification zone taking place to have any sustantial affect on the water column above."
A whole bunch of DSB'd tanks that maintain near zero nitrates would tend to be convincing. What is your explination for such denitrification if not the sand bed? Why does installing a DSB drop the nitrates, even though there is no forced exchange of the water?
I was not at all rude or condescending, I am just curious what your nitrate levels are now that you use this method of water changes.
"with the CPW concept you really don't care if you have denitrification taking place or not in the substrate. The concept is to physically remove the nitrates, phosphates, and other organic waste being produced"
Thank you. What were your previous levels of nitrate and what are they now?
You can just answer the question. No one will flame you, Honest!

 

[Randy Holmes-Farley]

Maybe you or someone else can explain something to me.....what makes people believe, even if you have some de-nitrification taking place below a couple of inches of the bed surface , that you have adequate water exchange rates between the water column above and that lower dead zone, to have any affect on reducing nitrates in the water column?

Regardless of how exactly the nitrate gets into those regions, it clearly happens. It has been demonstrated counless times when folks have added a DSB and found that nitrate levels in their established aquaria dropped from some elevated level (say, 5+ ppm) to less than 1 ppm. The same does not happen with a 1/2" sand bed.

 

[ldrhawke]

I was not at all rude or condescending, I am just curious what your nitrate levels are now that you use this method of water changes.
"with the CPW concept you really don't care if you have denitrification taking place or not in the substrate. The concept is to physically remove the nitrates, phosphates, and other organic waste being produced"
Thank you. What were your previous levels of nitrate and what are they now?
You can just answer the question. No one will flame you, Honest

My response was not meant to be either neither. That is why I used all the smiley faces. I was and still am curious.

Sorry I didn't answer your question.

My nitrates and phosphates are still non- detectable. Obviously there is something, but it is below the minimum of the test.

Also, regarding the 15% water change I did several days ago, in addition to the daily 1g of CPW, to see if I could improve and increase my ORP mv reading above the 325mv reading it showed. I had a very minor increase to about 335mv and then it dropped back down to the same 325mv range. It appears for my system the 1g per day wasting through the plenum is keeping the system stabile.

I still have some hair algae, but it has stopped growing and the clean up crew is working on the few small tuffs left near the top of the coral structure and light. That may never go completely away because it is so close to the light, a few inches, and the area always catches a little uneaten food before it goes over the overflow.

Regarding Randy's statement

Regardless of how exactly the nitrate gets into those regions, it clearly happens. It has been demonstrated countless times when folks have added a DSB and found that nitrate levels in their established aquarium dropped from some elevated level (say, 5+ ppm) to less than 1 ppm. The same does not happen with a 1/2" sand bed.

I believe very very low rates of denitrification is probably happening in a DSB, but I will bet the reef keepers that are also doing that good a job of husbandry in keeping the nitrates below 5ppm and the tester would have a difficult time saying they had a low reading because of not over feeding while they are doing the testing or if it was becasue of the DSB.

I still contend a DSB is a poorly designed and inefficient denitrification system at best. If it is doing minor denitrification it is not doing it very effectively. You have little or no control and a dozen ways to upset it.

Again, a question. At what depth do people feel that in a DSB, for all measurable purposes, it stops processing of waste?

Or to say it another way, at what depth do you feel you no longer get any measurable exchange of fluid and it is a dead zone? Is it 2", 5", 12"? At some point you are not getting any exchange or reintroduction of fresh food for either the oxic or anoxic microbes. At some depth, any additional sand added, has little or no significance in the biological process. What is that magic number?

And the next question. Is it logical to believe that if you positively transport food into those zones, that you can activate them into becoming an oxic or anoxic biological filter?

In contrast to a lot of peoples concern that a CPW system may stop or disrupt denitrification, I believe the odds are just as good, that it reactivates the whole bed depth into becoming more efficient oxic and anoxic biological filters by transporting waste into the full bed depth.

 

[ldrhawke]

Let me add another comment about my tank, that I feel adds some signifigance to my near zero nitrates and phosphates, my biological loading.

As much as I wanted it to be a reef tank and not fish tank, I am weak when I walk through the LFS and can't pass up an orphan. My tank is far too over loaded by good reef tank standards, but it is still maintaining near zero nitrates and phosphates.

In my 60g system, less gravel and rock space, I have a dozen fish. A Yellow tang, (3) Ocellaris Clown fish, (2) Cardinalfish, Algae Blennyfish, neon goby, (2)yellow headed jawfish, madarinfish, and a spotted madarinfish. I have seen reef tanks on the list tanks 10 times my size with less fish. With the amount of fish waste produced and excess food from feeding, keeping nitrates and phosphates down isn't easy.

I think you have to agree my set up, good or bad, is a good test for the CPW concept and the near zero nitrates and phosphates it has contributed in maintaining.

I say CPW contributes because I strongly believe like others that you should use every gadget you can to maintain water quality. I use a skimmer, filter media, and ozone also.

 

[Shoestring Reefer]

ldrhawke,

Have your jawfish built burrows? If so, do you feel they have affected the performance of your system?

 

[H20ENG]

I still contend a DSB is a poorly designed and inefficient denitrification system at best. If it is doing minor denitrification it is not doing it very effectively. You have little or no control and a dozen ways to upset it.

I totally agree. I have always believed that if you have ANY sulfide lurking below the bed, its gone too far anerobic. I dont think there is ANY place in a tank that can safely contain H2S.
And I also agree with you that there are many ways to upset a DSB.
I cannot answer what a perfect depth or grain size is, as there are far too many variables in each system.

 

[Clay Glover]

LDRHawke,

Thanks for sharing your ideas, experience, and expertise with us fellow reefers. I've read this thread and find your CPW approach worth trying and will apply it to my next tank. If long term disadvantages to using it do eventually come, they are easily remedied by discontinued use.

I have a question that you may be able to help me with. What are the potential disadvantages of using the plenum drain for higher volume, more traditional-type water changes of, say for example, 10% total system volume on a bi-weekly basis versus the smaller, but more frequent, 1/60th daily exchange you currently perform? I assume there are potential advantages to doing small, frequent drainings versus large, less frequent drainings, otherwise why would you do it this way, no?

If I understand you correctly, utilizing the DSB for bacterial denitrification is not a primary concern using the CPW approach. Maybe someone can advise me whether upon drainage, would newly introduced O2 into the bed kill denitrifying bacteria? Or just "de-activate" them until anoxic conditions are returned?

Thanks for your time.

 

[ldrhawke]

LDRHawke,

Thanks for sharing your ideas, experience, and expertise with us fellow reefers. I've read this thread and find your CPW approach worth trying and will apply it to my next tank. If long term disadvantages to using it do eventually come, they are easily remedied by discontinued use.

I have a question that you may be able to help me with. What are the potential disadvantages of using the plenum drain for higher volume, more traditional-type water changes of, say for example, 10% total system volume on a bi-weekly basis versus the smaller, but more frequent, 1/60th daily exchange you currently perform? I assume there are potential advantages to doing small, frequent drainings versus large, less frequent drainings, otherwise why would you do it this way, no?

If I understand you correctly, utilizing the DSB for bacterial denitrification is not a primary concern using the CPW approach. Maybe you can advise me whether upon drainage, does newly introduced O2 into the bed kill denitrifying bacteria? Or just "de-activate" them until anoxic conditions are returned?

Thanks for your time.

You're welcome....Your question as to frequency of change and concern for upsetting the oxic and anoxic bacteria in the bed go hand and hand.

The answer as too how frequent or infrequent you should drain the bed is based on a logical assumption that small frequent changes are better than larger more upsetting changes. On the other hand too small a drainage rate and the potential for a non-flushing action and uneven movement of fluid through the bed increases with low flushing rates. My flushing a pint every 6 hours is an attempt to maintain a flushing action and reverse flood the bed. Can it be done once a day at 4 times the rate and still work....probably.

Can it simply be used for weekly water changes..yes. But now you are disrupting the anoxic zone even more. Will it kill all the anoxic bacteria?..no. It will slow it down but will not kill it all. There is no way to get a uniform enough flow through the bed that can reach all the anoxic bacteria in a short duration flush. It will quickly re-establish itself.

The optimum rate and frequency will vary from system to system. There is a lot we don't know yet as to optimum mode of operation. It may be that weekly 10% flushing works better than uniform daily.

There are other aspects that have yet to be explored. As example: There may be some benefits to low flushing rates because they allow a drop in pH and help to keep and put back into solution phosphates building up in the bed. A lot more testing an monitoring needs to be done to maximize the potential benefits of CPW.

Good questions.....

 

[Randy Holmes-Farley]

I believe very very low rates of denitrification is probably happening in a DSB, but I will bet the reef keepers that are also doing that good a job of husbandry in keeping the nitrates below 5ppm and the tester would have a difficult time saying they had a low reading because of not over feeding while they are doing the testing or if it was becasue of the DSB.

Well, I disagree, and I think it is quite clear. Before DSB's became popular, many advanced aquarists had elevated nitrate. Most did, in fact, unless they resorted to denitrators or other schemes. When they added DSB's, the nitrate declined, ushering in the era of very low nitrate levels.

That's the only reason they became so popular: because the effect was fairly clear in many cases.

The thickenss required is a strong function of the grain size, IMO.

 

[darrellh]

ldrhawke,

How long does it take you to remove one pint with your siphon method? When I set up my new 90gal with a CPW bed, I'll use a powerhead with a variable onstriction valve on the disharge side to vary the flow rate. I was also able to find a digital AC timer with 1 sec resolution on E-bay, but unfortunelately I don't see any more available now. I think they were leftover timers from some other OEM project.

One other question. How do you balance the saltwater added and removed for CPW vs the freshwater make up for evaporation? Do you have any tricks for keeping the salinity automatically balanced?

Thanks,
Darrell

 

[ldrhawke]

I believe very very low rates of denitrification is probably happening in a DSB, but I will bet the reef keepers that are also doing that good a job of husbandry in keeping the nitrates below 5ppm and the tester would have a difficult time saying they had a low reading because of not over feeding while they are doing the testing or if it was becasue of the DSB.

Well, I disagree, and I think it is quite clear. Before DSB's became popular, many advanced aquarists had elevated nitrate. Most did, in fact, unless they resorted to denitrators or other schemes. When they added DSB's, the nitrate declined, ushering in the era of very low nitrate levels.

That's the only reason they became so popular: because the effect was fairly clear in many cases.

The thickenss required is a strong function of the grain size, IMO.

Randy,

As you know I respect your opinion. You been involved in reef keeping for a lot longer than I have. You are one of the best versed and have written technical papers that have become the bible of our hobby.

I don't disagree a DSB denitrifies. I don't disagree with the fact that substrate makes a good biological filter material and at some depth it becomes and anoxic biological filter. I have also read reports stating anoxic conditions can develop close as an inch of the surface in very fine sand and mud.

I am simply questioning, the belief of some that deep is good and deeper is even better. I question at what point beyond a couple of inches of substrate do you have usesless dead space that is of little good and potential harmful.

The whole concept of CPW is to take better advantage of the biological filtering ability of substrate and hopefully improve upon it's efficiency. In doing so, maybe even address the problem that many have experienced with what appears to be a limited life of the normal DSB, which even the most avid past proponents now appear to believe exists.

I believe the more biological filter surface we have in a tank the better.....as long as it can be controlled to some degree and doesn't end up as an anoxic garbage that can get out of control and burp poison back into the tank killing the coral.

My discussing the weakness in the conventional DSB concept doesn't mean I am against DSB's. I'm only adding a new twist by adding a degree of control and actually trying to salvage the DSB biofilter concept that appears to be on a down hill slide .

 

[ldrhawke]

ldrhawke,

How long does it take you to remove one pint with your siphon method? When I set up my new 90gal with a CPW bed, I'll use a powerhead with a variable onstriction valve on the disharge side to vary the flow rate. I was also able to find a digital AC timer with 1 sec resolution on E-bay, but unfortunelately I don't see any more available now. I think they were leftover timers from some other OEM project.

One other question. How do you balance the saltwater added and removed for CPW vs the freshwater make up for evaporation? Do you have any tricks for keeping the salinity automatically balanced?

Thanks,
Darrell

Darrell, Darrell, and your Brother Darrell....

I have it partially valved off and it takes about a minutes to remove a pint in my system.

The power head should work fine. Just make sure you put a syphon break at the top to keep it from draining all the water.

My fresh water make up is done with a float valve which opens the RO/DI line to the sump. The water drips in. NO SALT is required for the evaported water.

For the CPW drain I add about 1/2 cup of salt every day, a cup a couple of days, for every gallon I remove. I think doing water changes in this manner also helps to reduce shock to sensative coral that you can get with larger quantity water changes. I check SG regularly with a refractometer.

 

[darrellh]

Hi ldrhawke,

Nice, but there are (were) only two Darrells..the third guy was Larry. Do you really think their mom was that stupid to name all three Darrell.

My concern with removing/adding saltwater with an automated setup is that it will be hard to match the volume removed vs added. If this is always out of whack in the same direction, then the SG will eventually rise or fall. I realize I can monitor the SG of the tank manully and then adjust things accordingly, but I want to automate this as much as possible.

Thanks,
Darrell

 

[ldrhawke]

Hi ldrhawke,

Nice, but there are (were) only two Darrells..the third guy was Larry. Do you really think their mom was that stupid to name all three Darrell.

My concern with removing/adding saltwater with an automated setup is that it will be hard to match the volume removed vs added. If this is always out of whack in the same direction, then the SG will eventually rise or fall. I realize I can monitor the SG of the tank manully and then adjust things accordingly, but I want to automate this as much as possible.

Thanks,
Darrell

Just be thank full your mom didn't name you George. ie; George Foreman...

Without adding a controller for measuring and automatically adding concentrated salt solution, you simply need to be creative.

How's this for a Rube set up, if you have the space or a fish room. Get a large plastic container and pipe it to over flow into you fuge. Use the container for make up of fresh salt mix. Then take a heavy duty plastic garbage bag and discharge you CPW into it. Put the garbage bag in the fresh salt mix container.

Now as the tank is wasted it displaces the same amount right back into the tank.
:rollface:

If the fresh make up container is a 55 g drum, you will only need to make up a fresh salt mix once every couple of months.

Rube would love it.....:mixed:

 

[Randy Holmes-Farley]

I am simply questioning, the belief of some that deep is good and deeper is even better. I question at what point beyond a couple of inches of substrate do you have usesless dead space that is of little good and potential harmful.


OK, that's a reasonable question. Many of the reefkeepers that have added deep sand over the years (and later say nitrate drop) started with the usual 1/2 - 1 1/2 " of sand. So it seems clear (IMO) that deepr than that is useful. I have no idea whether 6" is "better" than 4", etc.

The depth obviously also depends on the grain size.

 

[Mojoreef]

Wouldnt it just be easier to remove the food/waste/detritus before it begins to be reduced?????


Mike

 

[Mojoreef]

Well, I disagree, and I think it is quite clear. Before DSB's became popular, many advanced aquarists had elevated nitrate. Most did, in fact, unless they resorted to denitrators or other schemes. When they added DSB's, the nitrate declined, ushering in the era of very low nitrate levels.

I dont know about that Randy. I dont think you could put that on the advent of sand in tanks. Thier were alot of things different back in those days, pumps, skimmers, testing equipement, education and so on. Maybe that the advent of sand gave hobbists more of an initial forgiveness of some husbandry mistakes.


Mike

 

[brentp]

Wouldnt it just be easier to remove the food/waste/detritus before it begins to be reduced?????

That is what I was thinking the whole time I've been following this thread.

 

[ldrhawke]

Wouldnt it just be easier to remove the food/waste/detritus before it begins to be reduced?????


Mike

Probably would be easier....lets see

With CPW you open a valve for less than a minute, manually or automatically waste a few pints to drain.....replacing the weekly water changes.......or...

You build a simple system to remove the solids. A good one I have seen uses 6 mixing eductors automatically sequenced to keep solids in suspension and the the flow goes to a double sock filter that should be cleaned out daily, Mangrove Tank to absorb waste, and in line carbon filter, a phosphate filter, through a multi compartment settling sump, and back into the tank. All controlled by an Octopus electronic controller.

Nah.......I'll stick with the complex CPW system.

Just kidding Mike...couldn't resist.:lol:

You have a great system. I only wish I had the space.