Dissolved Organic Compounds

[RickyV]

I am often asked why I do big and frequent water changes in a planted tank if the plants are consuming the excess nutrients. From what I have read on several forum posts is that there is a correlation between water changes and reduced algae and increased plant health. The most common reason said to explain this correlation is that water changes remove dissolved organic compounds.

This is my interpretation of the forum posts I have read so please correct me if I am wrong. Dissolved organic compounds include things like proteins, lipids, carbohydrates that algae can easily utilize as nutrient sources. Plants cannot utilize these dissolved organic compounds as easily (or at all?), and need them to be converted to inorganic nutrients like nitrates and phosphates to use them. Algae does not need to wait for them to be decomposed into these inorganic nutrients so they thrive with high levels of dissolved organic compounds.

I have also read that dissolved organic compounds are removed because they significantly increase the levels of aerobic bacteria which can reduce the oxygen levels in an aquarium. However is this really a concern with enough gas exchange in the tank? Or is it possible for the bacteria population to get so high that it would take a very unreasonable amount of gas exchange to supply enough oxygen to keep DO at optimal levels?

This gets me to my next question, if bacteria are consuming DOCs then they are competing with algae, which would be good? So would another method to assist in the removal of DOCs and thus reduction in algae be to use very large wet dry filters? Then plants utilize what is generated from the wet dry filter. I actually don't use any bio media in my planted tanks, however this is making me rethink that.

 

[Bradders]

Really keen to read the responses to this question! It is a great question.

Especially that you don't use biomedia in your aquarium environment - begging the question where all autotrophic and heterotrophic critters are colonizing.

 

[LMuhlen]

What I imagine on this topic, with no real evidence to back it up, is that the DOC trigger algae, but not necessarily is consumed by algae. I picture the DOC being processed by microbes and degraded into nutrients that both plant and algae can use, but the algae are "smart" and know that DOC will mean nutrients down the road and get triggered by it.

 

[bazz]

Really keen to read the responses to this question! It is a great question.

Especially that you don't use biomedia in your aquarium environment - begging the question where all autotrophic and heterotrophic critters are colonizing.

All of the surfaces within your aquarium is biomedia, I know biomedia is the given name for some porous bits of stone or round plastic balls but you are basically just providing a surface for bacteria to colonise, and it's then a case of providing the right conditions for the beneficial bacteria to proliferate. The magic of a planted tank is the plants themselves are already taking up some/most of the waste produced/administered but they aslo oxygenate the substrate creating a massive filter bed. The plants microbes live a symbiotic relationship and feed each other what they want. Then you have the surfaces of the leaves and hardscape even the glass if you haven't just cleaned it. These processes don't happen so freely in a well stocked fish only system this is why you would be required to use large amounts of filtration/biofiltration. Admittedly I'm using a 2180 on a 90x55x53 but I've had it for about 10 years now, there is only a single layer of SubstratPro in each of the three baskets and I'm mainly just using for flow. When/if it gives up the ghost I will replace it with a much smaller filter and turn the Nero 3 up a notch two.

 

[Oldguy]

Don't the answer, but I have found that DOC/mulm can trigger black beard algae. Others on this forum have found a similar correlation.
Perhaps the large water changes help reduce chemicals released by plants that reduce plant growth in other plants.
It seems to me that in simple terms: strong plant growth no algae; poor growth/dying plants lots of algae.
Not all plants play nicely with each other.

 

[hypnogogia]

So would another method to assist in the removal of DOCs and thus reduction in algae be to use very large wet dry filters? Then plants utilize what is generated from the wet dry filter.

I once used a trickle filter and experienced very little to no algae and had good plant growth.

 

[Bradders]

I once used a trickle filter and experienced very little to no algae and had good plant growth.

What is it about the trickle filter you are thinking will help with algae reduction?

 

[Wookii]

What is it about the trickle filter you are thinking will help with algae reduction?

Mainly increased average DO levels due to the nature of the filter (particularly where plants aren't saturating during the photo period). Significantly more efficient biological filtration due to microbes free access to air. Both indirectly can produce an environment which potentially microbes and plants rather than algae.

 

[Bradders]

Mainly increased average DO levels due to the nature of the filter (particularly where plants aren't saturating during the photo period). Significantly more efficient biological filtration due to microbes free access to air. Both indirectly can produce an environment which potentially microbes and plants rather than algae.

That makes sense - I had read that TFs are great for aeration but actually not very good with biofiltration without modification. But in a heavily planted tank the biofiltration is not going to be a key focus.

 

[Wookii]

TFs are great for aeration but actually not very good with biofiltration without modification.

Not sure what you mean, they are one of the best filters for biofiltration - many times more efficient than similar quantity of submerged media?

 

[Bradders]

From what I understand of TFs:

1. Great for aeration; in fact, it is very, very good. However.....
2. They typically have to use bio-balls with certain size grooves (which are not good biomedia), and the design means that water flow over the media is hit and miss compared to static configurations.
3. They do not outcompete canister filters filled with foam to the same volume as the TFs with bio balls.

 

[Wookii]

They typically have to use bio-balls

But they don’t have to - I use a plastic media (Oase Hel-X) to very good effect, which also seems to dispers the water well over all the media with a decent strainer grating above.

They do not outcompete canister filters filled with foam to the same volume as the TFs with bio balls.

I’m not so sure . . . But very difficult to measure. The fact that the microbes have free access to 400ppm of O2 vs 8ppm max (usually lower) submerged, makes a massive difference.

 

[Bradders]

But they don’t have to - I use a plastic media (Oase Hel-X) to very good effect, which also seems to dispers the water well over all the media with a decent strainer grating above.

I’m not so sure . . . But very difficult to measure. The fact that the microbes have free access to 400ppm of O2 vs 8ppm max (usually lower) submerged, makes a massive difference.

I think it's a fair point, and something for me to study more on. Maybe my next project over the EHEIM Pro 5 e?!

I read something about why bio balls are optimal for trickle filters, and K1-type media does not do too well as a replacement. The supposed optimum configuration comes from a % of K1-type and % of bio balls. But, I just don't have any first-hand experience apart from reading a few articles. They all do say they are fanatic aerators though.

 

[dw1305]

Hi all,

Not sure what you mean, they are one of the best filters for biofiltration - many times more efficient than similar quantity of submerged media?

@Wookii is right, that is why older sewage works used trickle filters, they have huge bio filtration potential.

From what I understand of TFs:

1. Great for aeration; in fact, it is very, very good. However.....
2. They typically have to use bio-balls with certain size grooves (which are not good biomedia), and the design means that water flow over the media is hit and miss compared to static configurations.
3. They do not outcompete canister filters filled with foam to the same volume as the TFs with bio balls.

That isn't right. Even if bio balls are suboptimal, they will still have enough wet surface area to work. It is the area of the gas exchange surface that matters, everything else is froth.

"Wet and dry" media is always going to out perform wet media. This is why marine aquarists regard trickle filters as "nitrate factories", they are right and it is an unalloyed good thing.

Nitrification is all about oxygen, and anyone who tells you different is misguided.

Cheers Darrel

 

[hypnogogia]

What is it about the trickle filter you are thinking will help with algae reduction?

As @RickyV surmises, the high DOC.

They typically have to use bio-balls with certain size grooves (which are not good biomedia), and the design means that water flow over the media is hit and miss compared to static configurations.

You can use any media you want. I used a combination of foam and Tunze Granovit (porous media). These days I’d use only foam.

 

[Bradders]

Nitrification is all about oxygen, and anyone who tells you different is misguided.

Thanks, Darrell. Something else to learn about!

But just a few questions I have in the back of my head:

This is why marine aquarists regard trickle filters as "nitrate factories", they are right and it is an unalloyed good thing.

What is a nitrate factory? Turning Ammonia into Nitrate is a 'process' - i.e., ammonia goes in, and nitrate comes out - assuming any filtration is doing its job properly. So, what is a nitrate factory?

That isn't right. Even if bio balls are suboptimal, they will still have enough wet surface area to work. It is the area of the gas exchange surface that matters, everything else is froth.

How much gas exchange is actually needed in an aquarium environment to ensure that nitrification is effective? i.e. when considering a trickle filter versus a pump outlet, although the trickle generates lots of oxygen, is it fully utilised or required?

older sewage works used trickle filters, they have huge bio filtration potential.

Is sewage work filtration a different world to aquarium filtration? i.e. Ammonia and toxic levels are far more significant than in an aquarium and, therefore, require significantly more oxygen and sheer girth to process?

 

[dw1305]

Hi all,

What is a nitrate factory? Turning Ammonia into Nitrate is a 'process' - i.e., ammonia goes in, and nitrate comes out - assuming any filtration is doing its job properly. So, what is a nitrate factory?

It just meant that there was always enough oxygen to allow the complete microbial oxidation of ammonia (<"TAN">) (NH3 / NH4+) to nitrite (NO2-) and nitrate (NO3-). As you say one molecule of TAN will end up as one molecule of NO3- (unless taken up by a plant). During the oxidation process you've liberated three protons (H+) and incorporated three oxygen (O) atoms.

Marine Aquarists <"didn't like the nitrate">, because they don't have vascular plants to remove it. I'm not <"bothered about nitrate">, I just want to get rid of all the TAN and NO2- as rapidly as possible.

Is sewage work filtration a different world to aquarium filtration? i.e. Ammonia and toxic levels are far more significant than in an aquarium and, therefore, require significantly more oxygen and sheer girth to process?

<"Not really">, they are the same basic process.

How much gas exchange is actually needed in an aquarium environment to ensure that nitrification is effective? i.e. when considering a trickle filter versus a pump outlet, although the trickle generates lots of oxygen, is it fully utilised or required?

You just need to ensure that <"the oxygen supply"> exceeds the Biochemical Oxygen Demand (BOD), trickle filters <"are an easy way of doing this">. The vendors of <"denitrifying media"> etc try to imply that you need "balance", but that is just b*llocks.

It is possible to have too much oxygen, but only in some <"very specific circumstances">.

cheers Darrel

 

[dw1305]

Hi all,

I read something about why bio balls are optimal for trickle filters, and K1-type media does not do too well as a replacement. The supposed optimum configuration comes from a % of K1-type and % of bio balls.

I'm not convinced the <"filter media has that much effect">. In Europe they use <"(Hydro)LECA">, it <"works really well">, but is a cheap product to buy and no-one is going to make much money out of it .......... <"https://www3.epa.gov/npdes/pubs/trickling_filter.pdf">

You need to watch out for "ponding" and "tracking", where the water always follows the same path and most the wet and dry media is "dry". I'm guessing that neither of these is ever going to be an issue for us <"Trickling Filter | SSWM - Find tools for sustainable sanitation and water management!">.

This is why sewage works use a rotating spray arm above a clinker filled bed.

cheers Darrel