# Kevin Novak: Anoxic Filtration



## loveflying1991

Has anyone on the forums tried using anoxic filtration as proposed by Dr. Kevin Novak? He has apparently developed a substitute for the more commonly used bio filtration model that not only removes Ammonia and Nitrite but also Nitrate, which lowers the need for water changes. 

If you look at his youtube videos, you can see that he is keeping discus in a planted aquarium, which he claims he has only topped off without performing major water changes for months. Please see below for a video of his on youtube. 

Kevin apparently developed this filtration for Koi ponds originally. 

Has anyone had success with this method of filtration?

Kevin also proposes with the use of such a filtration system not fertilizing with Nitrogen based fertilizers and phosphates. He only adds iron and potassium. From the looks of his plants this seems to be working for him. 
Any input regarding this method would be great.


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## MetalDemon

Bump, curious myself.


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## KevinC

What's the point of removing nitrates from a planted tank? Plants do that for you on their own. If your nitrates aren't being removed by your plants then you are way overstocked with fish or understocked with plants (or something else is missing). 

Plants need nitrogen in some form to grow and can't take it directly from air as N2.


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## FlyingShawn

Interesting concept, I haven't heard of it before.

How does this compare to something like Seachem Matrix? Do the kitty litter or laterite need to be recharged/replaced periodically? Is his iron/potassium dosing done for his plants or is regular iron dosing (in addition to the laterite) necessary for the "anoxic filter" as well?


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## Sobo

I have been following Dr. Kevin Novak's youtube channel for a while now. And although he does a few things that I find unnecessary, like rip up a perfectly good carpet of montecarlo and Dwarf baby tears because there is detritus buildup below it, a lot of what he speaks about is rooted in sound science, eg a plenum for any planted tank, fertilising during photo-period etc. 
For a planted tank, according to me the only disadvantage of anoxic filtration would be space. As a biocenosis bucket with a sump would take more space than a standard canister filter, especially since you have to increase the no.of buckets according to your livestock load. From his videos you can see that his backend is almost as large, if not larger than his front end.
The basic fact is that plants prefer ammonia to nitrates, so in theory, if his anoxic filter is working 100%, all his plant growth is solely due to ammonia as a source of nitrogen. From his recent videos, you can also say that his tanks are overstocked, but the argument he presents is that since his plant mass is keeping up with the ammonia supply along with the anoxic filter doing its job, there should be no detectable ammonia left in the tank. The anoxic filter converts through multiple processes, ammonia to gaseous nitrogen which is released to atmosphere. Not sure if the laterite plays a part in provinding a constant source of iron supply to the plants too. 

TLDR: Anoxic filtration too large of a setup for most people. Yes it works. No plants wont starve.


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## JusticeBeaver

I'm always a little wary of situations where people use Dr. in their title (except for Dr. Pepper). Anyway, the science is sound behind anoxic filtration however his design is pretty terrible. What you need to do is deplete the oxygen in the system as fast as possible to generate anoxic zones, so you would never leave it open to atmosphere. What he doesn't seem to mention is what happens to the nitrates in the system. There are really two paths that it could take, first it could be converted back into ammonia which his test strips convenient don't test but would explain his decent plant growth. Second it can be converted to nitrite --> nitric oxide --> nitrous oxide --> nitrogen (gas). But the absence of bubbles in his system makes me think that he's just converting stuff back and forth.


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## rainbowfish2

Sobo said:


> The basic fact is that plants prefer ammonia to nitrates, so in theory, if his anoxic filter is working 100%, all his plant growth is solely due to ammonia as a source of nitrogen.


It is "the basic fact" that plant uptake of NO3 is higher when a little ammonia is present. So total N uptake will be even greater when NO3 and NH4 are present. Any number of aquatic plant studies will show this. NO3, not NH4 is the standard in normal, unpolluted waters. Plants are adapted to perform better when NO3 is present. I do not understand this fascination with removing NO3 from systems... 





JusticeBeaver said:


> I'm always a little wary of situations where people use Dr. in their title (except for Dr. Pepper). ... What you need to do is deplete the oxygen in the system as fast as possible to generate anoxic zones, so you would never leave it open to atmosphere. What he doesn't seem to mention is what happens to the nitrates in the system. There are really two paths that it could take, first it could be converted back into ammonia which his test strips convenient don't test but would explain his decent plant growth. Second it can be converted to nitrite --> nitric oxide --> nitrous oxide --> nitrogen (gas). But the absence of bubbles in his system makes me think that he's just converting stuff back and forth.


100% correct Prof. Dr. Dr. JusticeBeaver. I hear all fish prefer a good jug of NO2 over NO3 every day.


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## jnboone

*more info*

There's another guy on youtube that describes anoxic filtration. Check out Jay's Aquarium. He has a four part series on it. He has a turtle tank he has not done any water changes to in two years. The high water quality and low maintenance combination is what has me most interested in this. I will be setting up a large tank in the near future that will be my first tank ever with a sump. I'm gonna give this a shot.

Bump: The litter/laterite never need to be recharged. He has baskets that have been filtering his koi ponds for years. His dosing is only for his plants.


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## king kong

Why the iron in the filter media?


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## Edward

Water column NO3 excess can be solved by adding essential plant elements assuming there are plants and the rest by denitrification. Denitrification can be done by filling a canister filter with BBQ lava rock over one inch in diameter. This can remove several ppm of NO3 a day while not changing other water parameters unlike the materials in the video.


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## Triport

He has some interesting videos but I always feel like I am being scolded for being an idiot when I watch them. Certain scientific types in the hobby sort of use their knowledge as a weapon and bludgeon you with it. There is a certain great planted tank guy who makes me feel the same way (but I am not going to mention any names).


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## houseofcards

Well it's common knowledge you need to be a doctor to have a successful planted tank. Dr Oliver Knott, Dr. Takashi Amano, Dr. Joe Planted Aquaria. That's why the hobby isn't bigger. Most will toil in mediocracy until they eventually give up. It would have been easier to get the doctorate.


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## JusticeBeaver

Triport said:


> He has some interesting videos but I always feel like I am being scolded for being an idiot when I watch them. Certain scientific types in the hobby sort of use their knowledge as a weapon and bludgeon you with it. There is a certain great planted tank guy who makes me feel the same way (but I am not going to mention any names).


My problem with his videos is that he doesn't really explain how or why anything works. He just makes it seem like if you're not doing what he's doing then you're an idiot.


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## voyetra8

BTW: He's deleted all but one of his videos, presumably because he got called out for his latest video straight up chastising folks for using vernacular / common names when discussing species. 

He repeatedly told viewers they "sound stupid" when they do things like call a _Plecostomus_ a "pleco". He wasn't joking either. He sounded genuinely angry. 

A user commented that if he was going to be a condescending pedant, he should at least pronounce _otocinclus_ properly. And that he sounds stupid. (He was pronouncing it oto-sink-U-lous.) 

12 hours later, and all his vids are gone. Coincidence?


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## Mpwallace1

Oh yes, the good Dr. I couldn’t watch much of them for the same reasons mentioned above. There was one there a few days ago I saw, in which he made you feel like a grade schooler if you dared use an API test kit, and not the one he or competent people in the hobby used. If his ideas work,then great, and I’ll follow the lead of any other fish fam on YouTube that explains things in layman’s terms. 


Sent from my iPhone using Tapatalk


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## Triport

voyetra8 said:


> A user commented that if he was going to be a condescending pedant, he should at least pronounce _otocinclus_ properly. And that he sounds stupid. (He was pronouncing it oto-sink-U-lous.)


Haha! That is really funny. I have to say as a horticulturist who worked in plant records at a botanical garden the mispronunciation of plant names (and fish names) drives me a bit crazy sometimes. I know botanical latin is difficult and even I am not always sure of the correct way to pronounce some plants but people don't even try and start switching letters back and forth. Or worse yet they apologize for mispronouncing something 30 times in their video. Instead of apologizing do a bit of research and try to say it at least close to correct. 

I've thought about making a video about pronouncing plant names but I doubt anyone would watch it and I would probably come off like a snob. :laugh2:


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## JusticeBeaver

Triport said:


> Haha! That is really funny. I have to say as a horticulturist who worked in plant records at a botanical garden the mispronunciation of plant names (and fish names) drives me a bit crazy sometimes. I know botanical latin is difficult and even I am not always sure of the correct way to pronounce some plants but people don't even try and start switching letters back and forth. Or worse yet they apologize for mispronouncing something 30 times in their video. Instead of apologizing do a bit of research and try to say it at least close to correct.
> 
> I've thought about making a video about pronouncing plant names but I doubt anyone would watch it and I would probably come off like a snob. :laugh2:


I'd totally listen to a 30 minute video of someone reading latin names for plants and fish.


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## Buzz1167

I was watching almost all of his videos, I just found the channel a few days ago. Did anyone else try it? It doesn't seem like a bad idea to have a plenum. However, I did find it a bit vague, how much flow he was suggesting to get from under there in order to provide the proper low oxygen conditions, at least if you plan for it and put something in place, if you want to play with the amount of water change under the substrate you can do so. And if you end up hating the idea, then the worst case is you block it all off, right?


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## Hyr

voyetra8 said:


> BTW: He's deleted all but one of his videos, presumably because he got called out for his latest video straight up chastising folks for using vernacular / common names when discussing species.
> 
> He repeatedly told viewers they "sound stupid" when they do things like call a _Plecostomus_ a "pleco". He wasn't joking either. He sounded genuinely angry.
> 
> A user commented that if he was going to be a condescending pedant, he should at least pronounce _otocinclus_ properly. And that he sounds stupid. (He was pronouncing it oto-sink-U-lous.)
> 
> 12 hours later, and all his vids are gone. Coincidence?


He was mostly responding to people who told him he was pronouncing it wrong and scolding him in the first place. He did reply to me in the comment section, when I told him he came off a bit harsh, and he said he didn't mean to be and was just frustrated with a particular user at the time, and that he would probably delete his video. Turned out he deleted all of his videos and re-uploaded only some. As for not explaining it, I believe he explained it to the point where you can draw your own conclusions; I mean sure, it isn't like a template layed out in a video, but he goes over the basics of how it works. He's an Ichthyologist, a doctor, and I understand he would be frustrated when he is criticized by ignorant people.


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## Riceman

I have a 75gal. tank with a 15gal. dry sump filter,it has about 25 bioballs and a 3" course
sponge filter with 2" of fine filter material on top.The only thing I do is top it off (about a gal. 
every 5 days ) and maybe 7 to 10 gallons are syphoned out,to get rid of built up detritus,
every couple of months.I've been doing this for around 5 years now and plants and fish are 
fine.
edit: I clean the filter material every month and a half.


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## voyetra8

Hyr said:


> He's an Ichthyologist, a doctor, and I understand he would be frustrated when he is criticized by ignorant people.


If someone's going to repeatedly tell people they "sound stupid" when using common names, he should make sure he's pronouncing the scientific names properly. 

The only ignorant person I see in this situation is the one throwing stones inside a glass house. :wink2: 

I will admit that a plenum seems to make a lot of sense to me - but this forum seems to think they are not needed. I may try one on my next build.


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## jnboone

Check out the videos on Jays Aquarium. He goes through the science of it all without sounding “preachy”. He says you can accomplish it simply with a deep substrate and excess plants. Nobody likes a know-it-all. Problem is most of those who are don’t realize it. I think Novak’s heart is in the right place.


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## houseofcards

It's funny because the late Takashi Amano, Oliver Knott and many other "names" in the planted tank world are far from scientists and I think their tanks look pretty good, much better than Dr. "I Found The Secret to Planted Aquaria"


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## JusticeBeaver

houseofcards said:


> It's funny because the late Takashi Amano, Oliver Knott and many other "names" in the planted tank world are far from scientists and I think their tanks look pretty good, much better than Dr. "I Found The Secret to Planted Aquaria"


They got to where they are because of trial and error though. Imagine what they would have done if they didn't have spend a bunch of time testing over and over again until they got the results they wanted. Deep beds to promote anoxic filtration certainly isn't new in the hobby (store like Ocean Aquarium in San Francisco apparently have been doing it for a while). In fact, sewage treatment plants have been doing it for decades now to clean waste water. The key is demonstrate effectiveness of new ideas by educating the public on why they work, so that future hobbyists can spend less time fiddling around.


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## houseofcards

JusticeBeaver said:


> They got to where they are because of trial and error though.


Exactly. That's why experience is king and not scientific theory that doesn't always work in a hobbyist setting.


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## Jeff5614

JusticeBeaver said:


> They got to where they are because of trial and error though.


And because their tanks don't look like an underwater corn field.


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## loveflying1991

Wow, I when I first started this topic thread I wasn't expecting to get so much response. Thank you for everyone who has chimed in. 

After making the original post, I decided to try and implement the annoxic filter in my own aquarium because I already had a sump and the room to play with. In the beginning, I didn't notice the nitrate levels dropping until about 2 months into the experiment. After passing the two month mark, I found that my nitrate levels have almost zeroed out at least on my test kits. Naturally, my ammonia and nitrite are also reading at zero and I have begun to remove the original biological filter media from my sump. So far the annoxic filter baskets have picking up the slack nicely, and I have seen no upticks in any of the ammonia, nitrate, or nitrite readings. 

I am not sure if zeroing out the nitrate is good for the fish or the plants as Novak purports in his videos, but the system does work as advertised to get rid of nitrate. 

Does anyone have opinions on Novak's claim that we don't need to fertilize for anything except micros, iron, and potassium? He says in one of his videos that he doesn't fertilize with nitrogen or phosphorous. I would appreciate if someone with more knowledge than I regarding plant husbandry could chime in on this point.


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## SingAlongWithTsing

loveflying1991 said:


> Wow, I when I first started this topic thread I wasn't expecting to get so much response. Thank you for everyone who has chimed in.
> 
> After making the original post, I decided to try and implement the annoxic filter in my own aquarium because I already had a sump and the room to play with. In the beginning, I didn't notice the nitrate levels dropping until about 2 months into the experiment. After passing the two month mark, I found that my nitrate levels have almost zeroed out at least on my test kits. Naturally, my ammonia and nitrite are also reading at zero and I have begun to remove the original biological filter media from my sump. So far the annoxic filter baskets have picking up the slack nicely, and I have seen no upticks in any of the ammonia, nitrate, or nitrite readings.
> 
> I am not sure if zeroing out the nitrate is good for the fish or the plants as Novak purports in his videos, but the system does work as advertised to get rid of nitrate.
> 
> Does anyone have opinions on Novak's claim that we don't need to fertilize for anything except micros, iron, and potassium? He says in one of his videos that he doesn't fertilize with nitrogen or phosphorous. I would appreciate if someone with more knowledge than I regarding plant husbandry could chime in on this point.


would you say your plants have been looking healthier now than befre you made the switch to an anoxic filter?

im tempted to try an anoxic filter in my sump but i'd be worried about my plants competing with the filter for NO3 and NH3.

edit:
i guess you can kinda circumvent the plant/bacteria resource competition if you layered your substrate like this:

something with high CEC (aqua soils, dirt, oil-dri, or kitty litter)
something with high iron content (laterite or maybe mexican red pottery clay)

it'll be an anoxic filter _in_ the tank in that case right?

edit 2: Jay's Aquarium with explanations on the anoxic filtration
https://www.youtube.com/channel/UCNJd0dyhX6-7xOHad6FTJ2Q


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## loveflying1991

My plants do look better, but I am not sure if that is a function of the filter or simply because my tank was rather newly setup when I started the experiment. 

My only question right now is how I should go about fertilizing the tank. I was doing ei dosing, but Novak seems to get away with just micros, iron and potassium, which seems appealing because of the fewer water changes he gets away with. Trying to figure out if I should try to fertilize the way he goes about it or if dropping phosphorous and nitrate will hurt the plants. As it is I am still doing the normal weekly water changes.

Bump: Also, as a side note, I did go on a vacation for about 2.5 weeks and the water parameters when I got back were still good, despite the lack of water changes...although I did get an algae bloom because my co2 ran dead during that time.


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## ecoaqaurist

houseofcards said:


> Well it's common knowledge you need to be a doctor to have a successful planted tank. Dr Oliver Knott, Dr. Takashi Amano, Dr. Joe Planted Aquaria. That's why the hobby isn't bigger. Most will toil in mediocracy until they eventually give up. It would have been easier to get the doctorate.


Well ... yes and no. I have two PhD's and still struggle in less than mediocrity. Then on the other hand. I spend 9 out 12 months in the hospital and my tanks go uncared for; then I come back to clean up the mess I left behind.

But that has nothing to do with my Phd's now does it. 

I find I ask more questions than provide answers and even the answers I might provide are full and complete without condescending. But then too I get accused of being arrogant for being informed and providing a full and complete answer with details. And sometimes when I ask a question and ask for details the same perception comes off.

Cheers,
Wes


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## houseofcards

houseofcards said:


> It's funny because the late Takashi Amano, Oliver Knott and many other "names" in the planted tank world are far from scientists and I think their tanks look pretty good, much better than Dr. "I Found The Secret to Planted Aquaria"





ecoaqaurist said:


> Well ... yes and no. I have two PhD's and still struggle in less than mediocrity. Then on the other hand. I spend 9 out 12 months in the hospital and my tanks go uncared for; then I come back to clean up the mess I left behind.


I'm not sure what your getting at. The people mentioned in the above are not Doctors. If you lifestyle keeps you away from your tank then most setup will suffer no matter who you are. You can have a tank without issue,but it would be extremely limited by light, plant types and lifestock.


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## ecoaqaurist

houseofcards said:


> I'm not sure what your getting at.


I'm sorry, I forgot where I was going ... lol


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## houseofcards

ecoaqaurist said:


> I'm sorry, I forgot where I was going ... lol


No problem, I was trying to figure it out and wanted to make sure I was OK, LOL


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## Viridis

Triport said:


> Haha! That is really funny. I have to say as a horticulturist who worked in plant records at a botanical garden the mispronunciation of plant names (and fish names) drives me a bit crazy sometimes. I know botanical latin is difficult and even I am not always sure of the correct way to pronounce some plants but people don't even try and start switching letters back and forth. Or worse yet they apologize for mispronouncing something 30 times in their video. Instead of apologizing do a bit of research and try to say it at least close to correct.
> 
> I've thought about making a video about pronouncing plant names but I doubt anyone would watch it and I would probably come off like a snob. :laugh2:



Out of curiousity, Do you tend to go for a more Classical, Ecclesiastical, or "modern" Latin pronunciation?

For example, do you pronounce "ae" as "eye" or "Eh"?



voyetra8 said:


> BTW: He's deleted all but one of his videos, presumably because he got called out for his latest video straight up chastising folks for using vernacular / common names when discussing species.
> 
> He repeatedly told viewers they "sound stupid" when they do things like call a _Plecostomus_ a "pleco". He wasn't joking either. He sounded genuinely angry.
> 
> A user commented that if he was going to be a condescending pedant, he should at least pronounce _otocinclus_ properly. And that he sounds stupid. (He was pronouncing it oto-sink-U-lous.)
> 
> 12 hours later, and all his vids are gone. Coincidence?


To be fair to Novak, I find common names frustrating too (and I'm far from a Dr.). "Black Tetra" could be 12 different species, but _Gymnocorymbus ternetzi_ is only one.


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## Triport

ae = eye

Can you give me of a word with ae in it that you would pronounce "eh"?


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## Wobblebonk

aeon aegis aerie algae... i haven't gotten out of the a's yet?

I don't know if it's quite eh but it's certainly not eyeon eyegis eyerie algeye

I guess you were talking about latin though :O in which case I have no idea.


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## Viridis

Triport said:


> ae = eye
> 
> Can you give me of a word with ae in it that you would pronounce "eh"?


For the record, I pronounce it "eye" as well (like the _y_ in fl*y*).

From my understanding (and the latin dictionary beside me) the ecclesiastical/ liturgical pronunciation is "eh", or like the _a_ in l*a*te or the _ay_ in s*ay*; as opposed to the Classical "eye" pronunciation. I've noticed quite a few people pronouncing it this way, for example:

_Chaeto(morpha)_ being pronounced "kay-toe' vs "kigh-toe". And on top of that, people pronouncing _ch_ like *Ch*eeto, but that's a separate thing.

I've also seen it with names like _Canidae_, even _aroideae_ for some reason. I'm not saying they are pronouncing it correcting, just that specific way.


granted, I'm not a latin scholar, so I very well may off here. Won't be able to take classes until I move, so this is based off the previously mentioned dictionary and a couple papers.



Wobblebonk said:


> aeon aegis aerie algae... i haven't gotten out of the a's yet?
> 
> I don't know if it's quite eh but it's certainly not eyeon eyegis eyerie algeye
> 
> I guess you were talking about latin though :O in which case I have no idea.


This brings up a topic I'm not sure of. People are also pronouncing _ae_ as "ee". For example;

algae pronounced as "al-jee"
Canidae pronounced "kanid-ee"

I wonder if this is some weird americanized pronunciation? Again, not a linguist.

Sorry for turning this thread into a latin thread. I saw latin pronunciation and got a little excited haha. :nerd:

I digress....


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## Triport

There are so many rules and it gets really complicated so I just try to follow some of the basic ones and if I am unsure I try to look it up to see if it falls under some weird exception. A lot of it is regional too and in some cases if there is a standard accepted pronunciation that is technically wrong it might be best to go with that if people won't understand you if you use the correct pronunciation. For example most people pronounce Aloe as A-low but oe is not a diphthong so the e at the end should be its own syllable. But if you go around pronouncing it A-low-ee with 3 syllables people will have no clue what you are on about. 

Algae isn't a scientific name so it wouldn't fall under the regular rules of botanical latin that I am familiar with. So regionally in America we generally pronounce it with a soft g and I believe in England it is pronounced with a hard g but I have also heard it pronounced with a short A sound at the end. 

Family names always end in -aceae which I was taught to pronounce -a-cee-a (both a's long) but I the more correct ways to pronounce them would be just -a-cee or a-cee-ee. I have never heard them pronounced a-cee-i.


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## Discusluv

ecoaqaurist said:


> Well ... yes and no. I have two PhD's and still struggle in less than mediocrity. Then on the other hand. I spend 9 out 12 months in the hospital and my tanks go uncared for; then I come back to clean up the mess I left behind.
> 
> But that has nothing to do with my Phd's now does it.
> 
> I find I ask more questions than provide answers and even the answers I might provide are full and complete without condescending. But then too I get accused of being arrogant for being informed and providing a full and complete answer with details. And sometimes when I ask a question and ask for details the same perception comes off.
> 
> Cheers,
> Wes


Excellently said.


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## ChuckM

I just wanted to add to this discussion (I'm a couple lifetimes away from a PhD. although some of my best friends have them) wrt Novak and this anoxic/anaerobic denitrification stuff. While I'm at it I also want to put in a plug for Jay's Aquarium (Youtube) as he best filled in the gaps that Novak opened. And in comic book form which is what I apparently needed.

We really can't discuss the work of the Dr. Novak without mentioning a predecessor named Professor Jean Jaubert and his "Monaco Method" or looking at the work the GARF group has done. Both are reef systems but just as applicable as the chemistry works the same. I drew on all these resources to build two on my own which I have no complaints of. I used Oil Dri baked clay absorbant mixed 3:1 with Ecocomplete on plenums they're both two years old now and if nothing else, the water is very stable, and I don't do a lot of water changes (maybe 30-40% a month, sometimes longer.


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## Betta Splendid

Just a heads up. Dr. Novak has started uploading new videos again. The new ones are on building a plenum for a planted tank.

I enjoy his videos and find them informative even though I run my tanks different. I hope he does an update on his main tank.


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## moke

the use of a plenum and a deep sand bed was hyped back in the late 90's for reef tanks. so not a novel idea.


with respect to pronouncing latin names, plantgeek.com (which is no longer available) gave pronounciation guides for most plants. eg; blyxa pronounced bly za, not blicks a. like wise, cryptocoryne not crypto cor ine, but crypto cor eye nee.


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## MassiveDynamic17

I've been inadvertently using an anoxic filtration system apparently. I chose montmorillonite ore for the substrate above the undergravel filter because I wanted to reduce pH. But apparently that's highly conducive to beneficial bacterial growth. plants grow great. i don't do water changes, just top-offs. I would have thought that'd preclude raising anything high maintenance, but I am content with the guppies and blue ramshorn snails (and others).


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## ChuckM

Had to look that up.
You mean Bentonite? How do you get it?
Plants look great, btw.


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## ChuckM

MassiveDynamic17 said:


> https://www.tractorsupply.com/tsc/product/ep-minerals-safety-absorbent
> 
> Apparently bentonite contains mostly montmorillonite ore? they use it to absorb oil spills. it's similar to old school cat litter. it's somehow conducive to the growth of beneficial bacteria.
> 
> Dr. Novak talking about the mechanism:
> https://youtu.be/6E4OZLEDijU



Oh!
I've had Safe T Sorb as a substrate for 2 years and didn't know it was Bentonite.
Works great!
BTW, see Jay's aquarium (YT) also for a very user-friendly guide to why it makes a great substrate for anoxic bacteria.


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