Posted: 2006.09.11(Mon)17:40 Post subject: Wet Dry Filters on Salt Water Tanks
This has always bugged me, so I'd like to bring it up for discussion. The new wisdom states that Wet Drys and other filters like it (HOB/canister/ect) will increase the nitrate in an aquarium, and promote the removal of them to reduce nitrate.
It is not that any less nitrate is produced when such a filter is removed, it is a question of what happens to the nitrate after it is produced.
When it 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 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.
That is the only article I could find that actually attempts to explain the phenomenon. My problem with this is simple: I can't see how it could work that way.
The bacteria that produce nitrate, and those that produce N2 require fundamentally different habitats to survive, one uses a great deal of oxygen, and the other requires anoxic conditions.
With the turnover in reef tanks approaching 50x (mine is 35x) those new nitrate molecules are not going to stick around long before they are thouroughly spread about the aquarium. The article suggests that deep crevices within the rock provide these anoxic conditions. While this might be true, it seems to not work as well as advertized, with the proliferation of DSBs and other methods of nitrate reduction.
Has anyone quantified the diffusion into these small areas, and if the locally higher populations on rock make a true difference?
Remote DSBs seem to be catching on. A foot or more of sand in a bucket. These appear to function well with almost no surface area for oxygen using bacteria, while it is by definition REMOTE from that live rock! That nitrate is coming from the main tank, not from the bucket.
Finally, for the common statement, "a wet dry produces nitrate too fast" or "nitrate factories" which would be preferable: relatively dispersed nitrate which will still be effectively turned to N2 by a deep sand bed, or allowed to linger longer in the water column as ammonia or nitrite? (The oddities of nitrite toxicity in saltwater aside), I would prefer neither in my water column if I could by using a "conventional" filtration method like the wet dry.
Hmmm, yes, funny thing is; I remember when wet dry filters were the "new wisdom."
Have I... "quantified the diffusion?"... well, no, and I've never considered myself an advanced aquarist or chemist sorry, but if your goal is simply nitrate reduction maybe we can help...
checked your profile, looks like freshwater info there, if you can give a little more system history and describe your setup and bioload, current readings etc....? _________________ Keepin' marines happy for 25 years
I don't know if this is what you are looking for but here's my 2CW
My understanding is that wet/dries (and other forms of filter based bio filters) are very good at trapping detritus and breaking it down to (end stage) nitrates. The perceived problem being that these forms of filtration trap and hold all the detritus within them and, unless cleaned frequently, will convert it all.
Thus the term "nitrate factories". One is trapping and converting all waste in the system.
Using L.R. in conjunction with protein skimming reduces the amount of nitrates produced in two ways:
a.) skimming removes organics from the water column before they are converted to nitrates
b.) L.R. does not trap detritus in the same way and "frees it up to be vacuumed or sucked out by the overflow.
The surface area of L.R. is also much greater than bio balls, ceramics etc... so it is more efficient at conversion / volume.
I don't quite follow the dispersion theory stated in the article for the same reasons you have noted.
I have a RDSB and I understand the reasoning for it as follows:
The depth of the sandbed allows for anoxic conditions where nitrite/nitrate conversion can occur as well as allowing a high density of available surface area (individual sand grains) for nitrates to fix on. This surface binding effectively removes them from the water column.
The concern with DSB's is that, at some point, the available surface area becomes saturated and can no longer fix nitrates. Then you would have a very efficient nitrate producer releasing nitrates back into the water column.
This is what is meant by a tank "crashing" (developing unsustainable levels of nitrates).
The RDSB was proposed as a way to thwart this. The theory being that, if rising nitrate levels were detected, the DSB could be disconnected and the sand substrate replaced.
As I said, I don't know if that helps but I'll offer it to the thread for discussion sake. _________________ Intelligence is not having all the answers; it's knowing how to think!
Mostly just theoretical. I don't like much of the way certain things opperate without.. any science or citation behind advice. It would be hard to do on a simple post, but many well respected articles seem to do that. Certain parts of that "wisdom" seemed a little funny, so I wanted to discuss it. Wet Drys could be nitrate factories for all I care, or know, I just wanted to discuss a few factors and see what people thought?
I've been working on diffusion and well, it involves intergrals to do what I want. I've got to borrow a calculus book before I get anywhere.
Good point on the detritus. Does that piece of fish poop or left over food being eaten by a detrivoir, or trapped in some rock differ from it being trapped in some bio balls? Most reefers seem disinclined ferret this stuff out of their rock work. In either case it will eventually turn to nitrate. I'm wondering if the additional step of going through a hermit crab really reduces the amount significantly.
As for my tank, its a 10 gallon with a yellow tailed damsel, a few astrea snails, and hopefully soon a few mushroom corals. Definetly not doing any denitirification, but that was never a goal of this tank. Getting the nitrates down from FO levels has been a pain, but a few more water changes and I should be set.
Does that piece of fish poop or left over food being eaten by a detrivoir, or trapped in some rock differ from it being trapped in some bio balls? Most reefers seem disinclined ferret this stuff out of their rock work. In either case it will eventually turn to nitrate.
I totally agree with you Psyfalcon.
What you put in must come out or be reused. In my personal opinion the whole bio balls rejection is unfounded.
I can under stand the logic behind the fact that if nitrate is converted to nitrite, next to the bacteria that converts nitrite to N2. Then nitrite should be less noticeable, since it's not necessarily mixing with the whole water body because the bacteria are situated so close, thus they pass the nitrite particles on, but this dose not mean it isn _________________ Years of fish keeping = Good advice
You want nutrient export as opposed to nutrient conversion. Trust me, there are a lot of hobbyists with stacks of live rock who THOUGHT their live rock would magically absorb any nitrates... it's all good for a year or two, but then the nitrates start soaring. Likewise, there are also a lot of hobbyists who have deep sand beds or 4 inch layers of crushed coral in their heavily populated displays which have become nutrient sinks and nitrate factories themselves... and the nitrates are soaring faster than the water changes can reduce it. This is an old story... again; you want nutrient export as opposed to nutrient conversion. Detritus and organic compounds must be removed before they can settle; and they must be kept to a minimum with less food, less fish. Even the best live rock, good water flow, skimming, reverse lighted refugiums with macros, sand beds, turbo-charged tumbling chaeto filters, etc. etc... whatever gizmo they come up with next week, ALL of it can be overwhelmed by overfeeding and overcrowding, poor husbandry and lack of export protocol. _________________ Keepin' marines happy for 25 years
You want nutrient export as opposed to nutrient conversion. Trust me, there are a lot of hobbyists with stacks of live rock who THOUGHT their live rock would magically absorb any nitrates... it's all good for a year or two, but then the nitrates start soaring. Likewise, there are also a lot of hobbyists who have deep sand beds or 4 inch layers of crushed coral in their heavily populated displays which have become nutrient sinks and nitrate factories themselves... and the nitrates are soaring faster than the water changes can reduce it. This is an old story... again; you want nutrient export as opposed to nutrient conversion. Detritus and organic compounds must be removed before they can settle; and they must be kept to a minimum with less food, less fish. Even the best live rock, good water flow, skimming, reverse lighted refugiums with macros, sand beds, turbo-charged tumbling chaeto filters, etc. etc... whatever gizmo they come up with next week, ALL of it can be overwhelmed by overfeeding and overcrowding, poor husbandry and lack of export protocol.
In a nutshell that is exactly correct. If you add it you must take it out. If the algae grows and the snail eats the algae then the nutrients that were contained in the algae are still in the system and your snail just released them when it pooped but now they are not contained in the algae anymore, they are free floating in the form of detrius.
There are many forms of export, use all you can find. Denitraters can at best only convert 50% of the available nitrate, it is much easier to remove the doc's than to convert them. Skimming, macroalgae and absorbing resins work and if used correctly can keep things in balance. Water changes help greatly as well. The less you add the less you have to remove.
Bioballs work as they are supposed to...they provide a place for bacteria to grow but the problem is they can only hold so much before the excess is released back into the water column. Skip the bioballs for a reef, you don't want the nutrients contained in the system, you want to export them, simple as that. Wet/Dry filters do the same thing, they get full of the bacteria and when they are full they release the excess back, this is OK for a fish only system but is usually the death of a reef with stony corals.
Limit the bioload and nutrient additions with food and it is easier to maintain. I break the rules with my system, I use a cannister filter and keep it clean. It contains nitrate absorbing resins and phosban and carbon. It gets cleaned ever other week. I do grow chaetomorpha and if I have algae in the display I keep it trimmed, it does grow and as it does it is consuming the nutrients in my system, my trimming is the export part. I overskim my tank with a skimmer that is very efficient and kept clean, that exports nutrients before they break down. I change 10-20% of my water every other week, that also exports nutrients. I do test my water so I know when my nitrates and phosphates are rising, if the testing shows little issues with nutrients I don't cjhange as much water. Know what is going on in the tank, it makes your corrective measures easier to deal with. _________________ Out on the road today...I saw a DeadHead sticker on a Cadillac...
110 Gallon DSA Pentagon
The degree of nutrients in the tank (and thus the need for removal) is also dependant on the type of system you are running.
As well as F.O. vs reef one can also look at varying flora and fauna within the reef.
A SPS dominant tank will need a nutrient starved water column to ward of unwanted algae blooms while a softy or filter feeding dominated tank may, in fact, benefit from a higher degree of nutrients.
As has been mentioned, I think too many people champion a "pet" method without recognizing that differing applications require differing methods and that most methods will work if applied correctly.
I am reminded of a LFS owner who took great pride in telling me I didn't need all those gizmo's for my tank as he only ran a large cannister on one of his display tanks (130 - 160 G.'s) and only cleaned it once every couple of months. Wow! Was I wasting my money???
I returned to his store some time later and every square inch of L.R. in that tank was carpeted in green algae!
But the tangs loved it _________________ Intelligence is not having all the answers; it's knowing how to think!
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