wet dry

I have been doing some research on filtration. It seems like anywere you go most LFS recomend wet dry filtration. I also see it advertised allot in internet stores however on most of the forums I have been on people discourge wet dry filtration. I would like to know how the people on this forum feel about it. I have heard it can cause an excess of nitrates. Is that true?

That does make sense. What is your opion? would you use a wet dry? Also would a refuge help eliminate the excessive nitrates? Thanks

Torghn is partially right.  It doesn't matter what type of filtration you use ammonia will be converted to nitrite and then into nitrates the same whether you use Live Rock, sand bed, or wet dry.  The difference comes after the conversion to nitrate.  Nitrate is remove when bacteria populates a low oxygen area (like a deep sand bed, or some places in live rock) and turn the Nitrate into Nitrogen.  This low oxygen area is not present in a Wet/Dry.

Torghn has a good understanding of the basics. Jake is an old pro.

A comment made about the production of excess nitrates is an interesting one. As good as wet dry equipment is for many people, the big problem is that the wet-dry or trickle filter does only 2/3 of the job. Those (nasty) bioballs are home to the bacteria that convert ammonia to nitrite and nitrite to nitrate and that's good! But the bacteria that eat nitrate cannot live in an oxygen rich environment. The trickling water in a wet-dry is very rich in oxygen. (The reason bioballs are "nasty" is that they accumulate detritus and then let go of it, sometimes all at once, causing major problems in the aquarium.)

The nitrate molecule is most toxic to inverts but not so hard on fish. That's why fish only tanks can do okay with wet-dry filtration, even with it's occasional crashes.

So… what to do with the nitrate molecules… The nitrate remains in the system until broken apart by low oxygen (anoxic but not anaerobic) bacteria. The resulting nitrogen gas is mostly absorbed into the water and is "gased off" at the surface. My understanding is that the oxygen part of the nitrate molecule is used by the bacteria.

Where can these bacteria grow?

Is there anything else that can handle this third stage of the process?

What if there were something that handled all three stages at once?

It is my understanding that the most effective filtration; the filtration that handles all three stages of the Nitrogen Cycle; occurs in the substrate and rock. It's natures way! All the other stuff, i.e.; outside filters, skimmers, wet-dry systems, adsorption media(carbon, etc.), ozonizers,
de-nitrifiers, ultraviolet (UV) sterilizers; always come up lacking, when compared to the biological activity of a good sand bed.

All of the current literature tells us about the complete bacterial activity, the "Nitrogen Cycle", which occurs in the sand bed and the rock. A substrate, if set up properly, handles all three stages from Ammonia to Nitrogen gas.

But you know what? The Nitrogen Cycle is only half the story of the filtration activity that’s going on in that microscopic world of sand and rock. An hour of the next WMAS meeting will be devoted to a discussion of filtration. I hope that the presenter makes biological filtration a major part of the discussion. And I hope that you can attend.

Thanks,
Mark R. Peterson
Founding Member and Treasurer, Wasatch Marine Aquarium Society
color=#800080www.utahreefs.com
Volunteer, The Living Planet Aquarium color=#0000ffwww.thelivingplanet.com
801-296-1563
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Salt Lake City, Utah

Mark,

Just one question! In your experiences what is the make-up of what you refer to as a  "A substrate, if set up properly, handles all three stages from Ammonia to Nitrogen gas."

Jody <SCRIPT language=javascript>postamble();

As you might see from the length of my posts, filtration is my major interest in the hobby. a few years ago I went on a field trip with my daughters school class. The two places we visited were the sewage treatment plant and the water treatment plant. I was fascinated.

After the post earlier today I kept looking for answers. I apologize for not doing more research before writing that post. It appears that within the last ten years there has been some activity in the scientific community to try and define just what species of bacteria are working the nitrogen cycle and where they are doing it. This work has been done for the sewage and waste treatment industry and those concerned with water ecology and pollution.

Here is what I have found out so far:

1. Ammonia is formed almost immediately as the fish waste hits the oxygenated water.

2. Ammonia is changed to nitrite in both aerobic and anoxic zones

3. Nitrite is changed to nitrate in aerobic, anoxic and anaerobic zones

4. Nitrate is changed to nitrogen gas in both anoxic and anaerobic zones

5. The bacteria that work on ammonia and nitrite are understood better than the bacteria that work on nitrate. Not enough studies have been done, but one study concluded that at least ten types of bacteria work on nitrate in anaerobic zones.

6. The studies do indicate that many species of bacteria other than the two that hobbyists talk about (nitrosomonas and nitrobacter) are working on the nitrogen cycle.

7. The nitrogen cycle has two parts:

Part 1 is known in scientific literature as the nitrification process:

waste Þ ammonia Þ nitrite Þ nitrate    Mostly occuring in aerobic and anoxic zones.

Part 2 is the process known as denitrification:

nitrate Þ nitrogen gas.     Most of it occurs in anoxic and anaerobic zones. Observation: The hobbyists understanding and use of denitrification is poorly lacking and almost nonexistent.

8. The bacteria doing this work are facultative, meaning they can live and reproduce under a wide range of nutrient concentrations. So when a fish dies or some excessive nutrient source is quickly added the bacteria can eat it up as soon as it appears. Observation: This explains what many of us have seen, or haven’t seen as the case may be, when a large fish dies and disappears without a trace or without even a blip on the screen.

Note 1: If this is where denitrification occurs it appears that the shortcoming of the wet/dry system is clearly seen! Are the tanks that use a wet dry and have sand and rock as vulnerable? I don’t think so and I will explain below in the hypothesis.

Note 2: This may point to a leading question of why nutrients/nitrates actually build up in the plenum rather than being denitrified! Especially plenums exposed to even dim light.

Hypothesis:

Here is a hypothesis based on the information above and my own observations:

Sand Beds especially Deep Sand Beds may be working better than anything we have ever seen because they offer a large anoxic and perhaps even a modest anaerobic layer. The times that I have broken a piece of live rock and found a black ring inside always caused me to wonder. I now believe that at about ¼ inch to 2 inches inside the rock, away from oxygen, the rock supports anoxic and anaerobic conditions. So anyone with "filtration equipment" that has rock and or sand or both is biologically supplementing the shortcomings of that equipment.

Hobbyists with rock and with sand deep enough to contain an anaerobic zone may be getting the best filtration we know of at this time. (If algae is growing somewhere in the system, then that’s not only a bonus, but in my opinion an absolute necessity for the health of the aquarium.)

Please understand, I am not at all saying the filtration equipment isn’t worth it, but rather that deep sand beds and rock may be the best form of filtration and perhaps more vital than any other filter.

Comments and arguments are requested.

Mark

A skimmer and RDP sump are excellent supplements to the sand and rock but not necessary.

Assuming that you have regular sized aragonite for the sand, if you added 2 more inches of that aragonite you would then have a place for denitrification which is occurring only in the rock at present. When denitrification is occurring in the rock only, the nitrates will tend to build up and run at higher levels which irritates the coral. Any increase of dead organic matter could lead to a quick bloom of algae. Water changes become very important in this situation.

As I said in previous posts, using about an inch or less of Oolitic can take the place of at least 2 inches of regular aragonite. It can be added a little at a time so that it sifts down through the aragonite. The external filter is needed at this time but as the sand bed increases in depth/surface area the external filter will be less important but still good as an extra. Mostly because of water circulation and aeration as it drops back into the tank. Water changes are also less important as the nitrates are better handled.

The organisms you currently have look good. After increasing the sand bed depth, add a little macroalgae and you could keep 4 or 5 fish a lot more coral and even a shrimp! Make sure you balance the fishes according to food requirements (meat eaters vs algae eaters).

Larger particles allow detritus to fall down between the particles and be worked on by the worms and insects in the sand. These consume the detritus cycling it into smaller and smaller particles that bacteria can work on. Without the larger particles the detritus swirls around on top of the fine sand providing a layer of nutrient rich water for cyanobacteria to grow in.

Mark