I’m putting this topic under “Algae” rather than “Plants”, although I was considering that this may be more of a plant health issue.

I’ve been running my tank without biomedia for many years now and, for purposes of pre-emptive questioning, the primary reason is to provide improved access to NH3/NH4 for plants while simultaneously reducing NO3 (plants’ preference for NH3/NH4 over NO3). For those interested; the nitrogen cycle can easily be maintained without biomedia in our filters, at least in a healthy planted tank with good biomass. I also have a heavy fish load.

However, I am now considering adding biomedia back in to my filter. While cruising, I stumbled upon this comment by @Edward a few years ago:

Of course, as I gradually reduced my biomedia, I was counting upon the biofilm to develop more fully on the surfaces throughout my tank, as I am sure that it did (and in the substrate), to take up any biofiltering slack that my plants couldn’t handle. Now, I’m wondering if some of the algae (mostly GSA) that we accept that develops on older, well-hidden, leaves may be a result of having this biofilm on the leaf surface. If this biofilm can be eliminated or, at least, reduced, do we also reduce the algae pest on these type of leaves?

Unfortunately, I can’t find much that supports this thought and am looking for a discussion that might expand my motive for putting the biomedia back in for this purpose. If anyone can provide some links discussing this (I can't find any of significance), I'd greatly appreciate it.

Of course, the biofilm is bacteria and the product of the bacteria might be a highly concentrated nitrogen source for algae, making it a preferred growth point for the algae. I would think that algae would also stick better to the biofilm than a surface not having it. If biomedia in a filter, being far more nourished with oxygenated water than the various surfaces in the tank, robs the BB in the tank of nutrients, do we get less biofilm on, e.g., our leaves? Does a leaf struggle if covered with increasing depth of biofilm, causing a cascading decline?

Lots of questions and some more:
- if we try to kill the biofilm in our tank (while protecting our biomedia), will algae struggle to develop?
- will leaves absorb nutrients better when not covered with biofilm?
- will biomedia, if sufficient in quantity, prevent any significant development of biofilm in our tanks?
- is there an allelopathic response from plants againts the bacteria?
- can algae even stick to anything without the biofilm first in place?

Lots of learning likely to follow - subscribed!
FWIW, I have a rather large amount of Eheim Substrat Pro, and Eheim BioMech in my AquaTop CF500 canister filter, along with a "heavy fish load" - basically the opposite of your setup.
Will be interesting to see where this thread goes :-)

Using Poret foam as a corner filter and that's it.
I sterlize the foam @ every swap out.
Small phish load and heavily planted.
When the swap is made I never detect ammonia.
Been ignoring the "cycle" idea for years with heavy planting.
If a heavy phish load was present a different song would be sung.

Fact: Leaves absorb nutrients better when not covered in anything.
Just went through this with last algae attack.

Biofilm: None that is noticeable and extremely clean glass.

Allelopathy: Has this really been proven in submerged plants?
I am unknown on this one, but if my healthy plants are sending death vibes to algae I'm good with it.

Just some thought from my 80G tank.

I would think so as well, but do we know for sure?

Another problem: can we tell if and how much biofilm might be on the leaves? We can sometimes see it on glass and, as @Edward said, accumulating in our tubing.

Not that I have been able to find. Diana Walstad claims it's everywhere and I have encountered a lot of 'confirmations' from hobbyists that Egeria/Anacharis does it.

I'm subscribed, hoping to see more info/viewpoints on this subject.

Looks to be an interesting topic. I have been one to load up my canisters with bio media, and do have a heavy fish load. That said, things are relatively balanced in my tank.

I'll be following along!

I’ll offer a suggestion for a process to look at this, although I don’t have the tools. I think we’d be looking at two tests.

The first test is to see if we can stop or, at least dramatically reduce, the formation of biofilm anywhere but on the biomedia in our filter, ignoring the algae issue until this is accomplished (although it would undoubtedly also kill all algae short term):

1) Kill all of the bacteria that comprise the biofilm without permanent damage to any other life in our tanks …no small feat. What would it take to do that: H2O2, glut, antibiotics, etc, and how much for how long? We'd have to wait for new plant growth to replace the old, biofilm covered, leaves. The filter, of course, can be removed/shut off during treatment. Would just adding increasing amounts of biomedia eventually starve all tank-based biofilm? How long would that take? I would expect that a microscope, in the right hands, would easily show if any bacteria existed on surfaces.

2) Find the right amount of biomedia, if such a sweet spot exists, to develop a biofilm large enough to grab a sufficient amount of the organics, via trial and error.

3) Repeat the testing until we see that no/arrested-at-low-levels biofilm ever develops. How long a period of time is enough to say that the biomedia is doing this?

If this sustained knockdown of the biofilm can’t be verified, there may not be any point in going to the second test. However, if it’s tried by enough people and positive results are seen , then maybe that’s a win.

The second test, of course, is to watch to see if any algae develop once we can verify that the biofilm is either gone or greatly reduced. We will also want to watch our plants for changes and look for nutrient demand changes that might occur if there is no/little biofilm on the leaves.

Now, we wait to see if some better ideas appear. Maybe more importantly, if anyone is aware of this having being tested before.

For what it's worth I was Phishless for quite some time.
A density of plants that many would want for their own.
Daily dosing urea in large amounts only to see no NH3/4 present within a couple hours and never register NO2.
NO3 dosing was dropped in order to not accumulate nitrates.
I later kept 10ppm NO3 in the water column @ all times with KNO3 dosing.
Was not happy with this parameter NO3 @ zero.

So during this time was any beneficial bacteria formed, I doubt it.
But over a large amount of time, say 3 months maybe some was formed.
But then I sterilize the Poret foam again and back to zero BB.

The problems would arise from the varied phish load that many keep.
Also heavily on the feeding schedule and many overfeed their phish.

During the period where you are guessing that no biofilm was formed, did you see any difference in algae formation than at other times? IMO, the focus is on the slow-forming GSA on the older leaves that even higher PO4 dosing doesn’t prevent.

Nitrifying bacteria are, literally, in the air, just waiting to fall into some water and start eating organics. So, you must have had BB in your water. The question is: how much organics were in the water to eat? Wouldn’t you think you would have had enough organics from the large biomass to get a biofilm going?

I, too, was dosing urea, but at 1ppm NO3 equivalent (now at .5 equivalent NO3), no NO3 dosing and with a heavy fish load and intentionally overfeeding. NO3 holds at around 5-10 and no NH3/NH4 is noticed (may be some spikes when I’m not looking). When I’m not disrupting the balance, I rarely get hair algae (including BBA) or GDA. It’s the GSA that forms on the elderly leaves that makes me think this is a biofilm issue, otherwise why would the leaves let algae grow on them if they have all of the mobile nutrients they need?

These are 2 good reads on AOA, 2nd study delves into how they differ in regards to how they respond to environmental factors including ammonium levels, light, PH and oxygen levels. Apparently AOA don’t like light where AOB doesn’t care and would explain why the 1st study showed that AOA dominated inside most aquarium filters. Increasing/decreasing oxygen levels had little effect on AOA populations while AOB showed a direct correlation to oxygen levels.

https://www.dropbox.com/s/k82xqkku1t...23281.pdf?dl=0

https://aem.asm.org/content/78/16/5773

biofilms are everywhere and it's sort of a 2 edged sword..

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3759889/

https://link.springer.com/article/10...201-016-0415-2



https://www.int-res.com/articles/ame_oa/a058p079.pdf
https://microbewiki.kenyon.edu/index.php/Stream_biofilm

not sure of autotrophic bactr .on leaves though..

I took a little different read on this:

Very interesting. So, very little, if any, bacteria (esp. Nitrosomonas) involved in freshwater nitrogen cycle after all …but only where NH3 dominates. an NH4 abundance means that bacteria, and not archaea, dominate. I guess we have to now focus on BA (Beneficial Archaea) where NH3 is involved.

Generally, then: AOA above pH of ~7 and AOB below pH ~7. Could an implication from this be that, if we are going to run tanks below pH 7, it is important to cycle them that way to develop AOB vs. AOA? If we keep pH above 8, which is commonly recommended for cycling, we may not have the necessary AOB when we drop pH below 7?

Also, does this mean that anaerobic reduction of nitrates is better suited to NH4 conditions if bacteria, in fact, aren’t found in NH3 environments?

Great find @DaveKS!

We still have the issue of the biofilm question but, it seems that flooding an aquarium with near-UV may kill the biofilm in an NH4 environment (probably near-visible is even deadlier), but NH3 environments may not respond to this energy region.

Also: the archaea weren't mentioned as having anything to do with NO2, or did I miss it? So, in an NH3 environment, bacteria that consume nitrites must still exist.

More good stuff. It indicates that biofilm formation can be impeded by a lack of organics. Maybe there is a blunt edge on the beneficial side of that sword if we supply the traces as well as the biofilm colony does.

Questions (probably rhetorical):

- How much benefit does the symbiosis of the biofilm provide to a plant through the leaves? Maybe the plant can still thrive without the biofilm.
- Will BB struggle to develop well enough as biofilm on plants if organics are rapidly provided to the biomedia in the filter?
- If the biofilm, itself, acts to protect the bacteria from things such as UV, will a dose of something such as H2O2, glut, antibiotic, etc., disrupt this protection enough to allow near-UV or just into the UVA-A range to destroy the formerly-protected bacteria in the biofilm?

Looking elsewhere for a connection between “stream biofilm” and algae, it seems that algae actually becomes a part of the biofilm. So, it seems increasingly likely that destroying the biofilm will eliminate an important operational base for algae.

Here is another read and newer than some of the others.
https://journals.plos.org/plosone/ar...l.pone.0113515

While this is all quite interesting material and some occasionally gets forwarded to me by scholarly scientific hobbyists (link provided) my search for knowledge is not in this direction so much.
I certainly cannot sample this bacteria let alone perform DNA analysis on it.

No, I can't analyze for live bacteria either and I doubt that any of us can.

I'm thinking that the way I'm going to try this is to first build the biofilm in my filter (have some Biohome Ultimate on the way). Then after a month or so, do a heavy dose of Excel (it does kill bacteria - I'll remove the biomedia) at about 3 ml / gal, which I know to be safe on a one-time basis. Finally, I'll place this open sterilizer: https://smile.amazon.com/Coospider-A...s%2C148&sr=8-6, in close proximity to the plants (within 8-10 inches), which will require placement adjustment about 6 times throughout the tank. It only takes about 10 seconds for UV-C to kill bacteria so, I figure a minute in each placement should do the job thoroughly without harm to other life. Then, we'll see how the plants do and whether the good 'ole GSA returns to the old leaves.

I'll have plenty of time before implementing and may make some course corrections depending upon what further develops in this thread.