Denitrification using car sponges

[Snug]

My aquarium is bare-bottom without live rock.

The sump is higher up than the main display and is filled with car sponges.

There's a 3w powerhead with tubing that moves water slowly to the sump past the sponges and gets gravity fed back into the main display.

The end of the tubing to the sump has a plastic attachment similar to a showerhead. It's filled with densely packed cotton wool that's changed daily, so no detritus can get to the sponges. I also dose vodka.

My sponges are free floating and are not densely packed together. I'm thinking about adding more sponges so the water has to slowly flow through them instead of around them.

This thread is specifically about car sponges. I figured they will work similar to a deep sand bed as they have an massive surface area for bacteria to colonise.

Each sponge is 7.5" x 4" x 2".

I have two scenarios to discuss.

One.

If the sponges are not densely packed, the water will flow past them, where there is less resistance, so I would imagine the denitrifying bacteria would only live a few millimeters into the sponge surfaces and the rest of the sponge would be anoxic without hardly any water movement within it.

Two.

If the sponges are densely packed into the sump, the slow flow of water would be fored through each sponge and the entire sponge would denitrifiy the aquarium water.

If that was the case, deep sand beds would be pointless as they would turn anoxic a couple of inches down. You may as well just have a 3" sand bed for denitrification or force water slowly through sponges. I think denitrification would occur less than a centimeter into a dense car sponge.

In scenario one, if you were to inject the center of a sponge with say, 5ml of black ink, how long do you think the ink would remain in the centre? If it actually bled out, then scenario one might still be viable, but I would imagine the ink would stay in there for weeks.

You might be able to upgrade scenario one by cutting each sponge in half so they're 1" thick instead of 2" which might remove anoxic zones.


Which scenario do you think will have the best denitrification capacity?

I think scenario one would act like scenario two if it had 10x the number of sponges.

 

[Snug]

I forgot to add and can't edit my OP,

I'm currently dosing 0.8ml per day of vodka to my sump of sponges.

I dose 0.4ml at 4am and 0.4ml at 4pm (I wake up early to commute).

This is added to an inverted 250ml syringe full of water and slowly dripped over 12 hours at a time.

If you dose vodka directly to your aquarium, you can lose fish. Slowly administering it to a sump with media means that the denitrifiying bacteria get to it before the fish do.

 

[Snug]

I think I've answered my own question.

Scenario one needs lots of flow and scenario two needs very slow flow.

Obviously, the more sponges, the better. Scenario one seems the best choice as scenario 2 will become anoxic as the water flows to the other end of the sump.

Scenario two is basically one big sponge with unpredicable areas where there are gaps. where the the water will flow in the path of least resistance.

It would be better to have many free floating sponges with good flow to remove anoxic zones.

 

[Oldreeferman]

No live rock just sponges?
As i once a month flush out the holes & crannys in my live rock while filtering right before the water change I can't imagine how one would keep sponges from becoming nitrate factorys quickly as they are acting similar to just thick filter pads filling up with gunk not just bacteria.
I think that this is why this setup is not seen in use normally, one could squeeze & rinse them all out in old tank water at least weekly but that would become a labor intensive chore where as just blowing off the live rock in a refugium would be so much easier and allow flora & fauna to grow on the rock as well another benefit.
I do know i have to clean & replace my filter bag every 2-3 days or its a real mess, id never even contemplate a sponge after what i see on my filter, maybe your mileage will vary if the bio load is really really low?
I also like you dose, tho I use 3 types of carbon sources vinegar, sugar, and methanol pre-mixed to grow a variety of bacteria verses just one type, and it helps vastly against nitrates better even then filtering so there is that to consider along with a filter sock and without the sponges.
Personally from my exp and what ive seen setup if i wanted a bare bottom DT id have a refuge same size as the DT full of live rock for ease of cleaning and maintenance.
Just what ive noticed after several yrs. of dealing with cleaning, filtering, and bacteria needs.

 

[Michael Hoaster]

Well, this is something different! I think you stand to learn a lot from this, and the rest of us following can learn from it too. As Thomas Dolby once said, "SCIENCE!"

From what you have said so far, it appears you are attempting to achieve nitrification and denitrification in your sump using large, synthetic sponges, correct? I have no idea which scenario will work best, but you could try one, and test your water to see the results. I'm more curious about your goals for the overall system, and why you are doing it this way. Trying to save money? Contemplating revolutionizing the hobby? Got a great deal on sponges?

Good luck with your experiment! I wouldn't look at it as a pass or fail thing, but a great opportunity to learn. Please keep us apprised.

 

[Snug]

Thanks, I'll keep you updated.

I used the word anoxic incorrectly, thinking that it meant that there was zero oxygen, but the correct word is anerobic to describe that condition.

'Anaerobic = total absence of free oxygen (O2) or bound oxygen (NO2, NO3)

Anoxic = absence of free oxygen, but presence of bound oxygen'

https://www.researchgate.net/post/What_is_the_difference_between_anaerobic_and_anoxic_conditions

From what you have said so far, it appears you are attempting to achieve nitrification and denitrification in your sump using large, synthetic sponges, correct?

That's correct. The sponges cannot get dirty as they cannot be squeezed or rinsed so the water to the sump has to be heavily prefiltered. I have a Tunze keeping detritus in suspension in the main display so I only have to change the cotton filter to the sump. I want an aquarium that requires hardly any maintenance and I'm thinking a 200 litre sump with 100 free floating sponges might do this.

The sponge material provides an enormous area for bacteria colonization. A two inch diameter by six inch long sponge is equivalent to a gravel bed one inch deep and three feet square.

So times that by 100 sponges.

Portability: A sponge filter may be moved easily from one tank to another, and will quickly become colonized if placed in a well established tank first. It is easy to protect the bacteria from medicating the tank by simply removing the sponge filter and returning it once the medication treatment is done.

 

[Snug]

I found this interesting read,

'Biological filter capable of simultaneous nitrification and denitrification for Aquatic Habitat in International Space Station'

https://www.sciencedirect.com/science/article/pii/S221455241400008X

 

[Snug]

No live rock just sponges?
As i once a month flush out the holes & crannys in my live rock while filtering right before the water change I can't imagine how one would keep sponges from becoming nitrate factorys quickly as they are acting similar to just thick filter pads filling up with gunk not just bacteria.

This is what I want to avoid. Even though the water to the sump is heavily filtered with tightly packed cotton wool, the bacterial mulm will still form inside the sponges. They can't be rinsed or squeezed. To transfer a sponge to another system, I would have to scoop it into a container of water without exposing it to air. I think I might tag each sponge so I know how long they've been in the sump.

To stop the sponges from getting clogged with bacterial mulm, I would have to give the sump a lot of flow. Enough to keep them slightly unclogged, but not enough to upset the anaerobic zones within them.

I think it would be difficult to keep detritus out of a sump of sponges if it was fed by an overflow.

 

[Oldreeferman]

Bacteria are pretty resilient if not badly shocked by extreme temp swings or a major environment change that lasts any extended time. Lots of live rock is shipped just wet out of water & holds its own well if not temp shocked the bacteria is still intact within, you can google discussions about this practise.
The only thing ive ever read that is immediately effected if exposed to air are real living sponges, a real headache for all except professional Aquariums so are avoided by regular reefers usually due to this fact.
I always wash out my filter sponge with old tank water & reuse it due to the bacteria it holds and a few seconds out of the water back & forth never effected it other then removing the gunk buildup so allowing the bacteria again access to full water flow.
My DT never reads any ammonia or nitrites but again i have live rock so i can afford to mess with anything in it without any effects.
Id like to see pics of your setup & any testing data months down the rd. of the experiment also as mentioned since its a unique idea and interesting to follow.
You answered a question i had which was how do you intend to filter the sponges or avoid them becoming clogged over time.
I tried this in my early days & found the floss a pita to have to replace constantly and it really clogged fast due to the superior filtering it gave me but it also had a high chance of over flowing when it held all it could & stopped filtering so in the end it did not serve as an easy alternative to simple live rock which i considered beautiful in my DT with coralline everywhere in different colors and the vast flora & fauna verses an empty looking DT.
Now on the plus side some possible DT issues are kept at bay such as vermetid snails & other pests that can/and usually do come in on live rocks or sneak in on frag plugs so your idea has good warrant on this for a fish only DT but some housing & sheltering is still necessary for happy low stress live stock so id have to see pics of the setup the live stock and the data down the rd. to fully grasp what you are trying to attempt here and why.
With no examples of the total expected end bioload you intend to house talking about bacteria is moot really until its a known factor due to so many variables like fish only, SPS only, mixed reef, softys only, etc.....
Anyway i think the real issue you will have to deal with is the floss filter it gets old fast. Id like to hear how that is dealt with long term easily.

 

[Snug]

With no examples of the total expected end bioload you intend to house talking about bacteria is moot really until its a known factor due to so many variables like fish only, SPS only, mixed reef, softys only, etc.....
Anyway i think the real issue you will have to deal with is the floss filter it gets old fast. Id like to hear how that is dealt with long term easily.

Correct. There are many other ways to reduce NO3. I'll update when/if I have usable data.

I don't want to rely on the porosity of LR in the DT for denitrification.

 

[Anemone]

One thought I had - I wonder if sponges might be treated with an anti-microbial/anti-mold compound to keep them "fresh" longer. I have no info that they are, but this reminds me of people using dehumidifiers for fresh make-up water only to find out the dehumidifier coils had been treated.

Kevin