[hoppycalif]

I have been reading and re-reading Diana Walstad's book, "Ecology of the Planted Aquarium", because I've reached the age when low maintenance is my prime requirement for continuing to have an aquarium. While reading the book I became very interested in the sections about algae, primarily one concept: algae require minute quantities of nutrients, including iron, but iron is pretty hard to find in the water. This now has me obsessing about whether we can make a big stride towards avoiding the most obnoxious algae attacks if we make the effort to keep iron out of the water.

I have for many years been using the EI fertilizing method or modified versions of it. Those require that we dose trace element mixes, which contain iron as an important ingredient. From the book, it appears that this is like giving algae a spare key to our "house".

Algae, unlike plants, cannot get to the iron in the substrate, whether it is soil or gravel with substrate fertilizing. So, it seems like if we did all that we can to limit the iron to the substrate, our algae problems would be much easier to manage. Included in that idea is the fact that light can make what iron is in the water more available to algae, if the light is intense in the 500nm or shorter wave lengths. That means light in the blue-green to UV range.

I'm still digesting this concept, and doing more reading, but I'm wondering if many people have tried to use this as an algae control method.

 

[mistergreen]

Non substrate feeding plants would have a hard time if all the nutrients are in the substrate. So you limit your plant selection which is fine but some people prefer others.

Also if your water's pH is 7+pH, the chelated micro/iron only lasts a few hours before they become unavailable to plants & algae.

I've found a jungle tank packed with plants always control algae.

 

[hoppycalif]

A heavily planted tank, with healthy growing plants, might keep the level of iron in the water low enough to reduce the algae problems. I know it is well established that lots of healthy plants seems to discourage algae, but why? One possibility would be the reduced iron in the water. The chelated iron we dose has a very short life in the water anyway, because the plants quickly remove most of it.

It's true that relying only on the substrate for plant nutrients does limit the variety of plants you can use, but Diana Walstad suggests that if you do a dry start with the stem plants, they will grow a good enough root system before the water is present to allow them to continue to grow well with just substrate nutrients. I have never tried any of these ideas so I don't know how well it will work for me.

 

[mistergreen]

I've had a NPT 10G tank I've topped of but haven't done any maintenance for years. I don't dose anything; just fish food. It has minor clado but I let it be. Part of low maintenance is to be fine with algae.

A 10G seems to be a perfect size.

 

[hoppycalif]

The interesting theory Ms Walstad mentions in her book is the effect of strong light on iron. Algae are limited by how much iron they can take up, and all of it has to come from the water. One thing many of us notice is that the more intense our light is, the bigger our algae problems are, so we tend to use no more light than we have to. But, if light causes momentary increases in available iron, that would explain why more intense light leads to more algae. And, it suggests that if we can keep the iron in the water down to near zero, more light won't lead to more algae. And, if that level of iron in the water is essentially zero, we shouldn't have more than trivial algae.

I still wonder if anyone has made an effort to apply this, by never dosing iron in the water. I do vaguely recall that a few European hobbyists have promoted limiting iron to a much lower level than most of us have strived to have. I wonder if that is related to this?

 

[mistergreen]

How does light make iron more available?

You'll have to make a distinction of which 'iron'... Iron Oxide could be ubiquitous but can't be used by plants or algae.

 

[hoppycalif]

To quote Ms Walstad, "Intense light makes iron more avaliable for algae in a process called "iron photoreduction". I googled it and found https://www.sciencedirect.com/science/article/pii/S0967064504001961 and https://www.sciencedirect.com/science/article/pii/S0304420304002257 and https://www.semanticscholar.org/pap...ball/3ca1ea94ff0b75da677ca746f08dcbb65ce512ac and https://www.advancedaquarist.com/2002/10/chemistry

Another quote from Ms Walstad: "I would be more concerned about Fe than P (or nitrates). That 0.1 ppm Fe level may be stimulating algae."

If I recall correctly, the photoreduction process separates Fe+++ from any chelator for a very short time, but enough for algae to grab the iron.

 

[Maryland Guppy]

FWIW I've been measuring Fe consumption in a high light CO2 tank for 12 weeks.
The daily average of a densely planted tank is .015ppm of Fe per day.
My dense planting is quite heavy!

 

[hoppycalif]

A high light tank, with CO2 being added, will cause the plants to grow too fast for the substrate nutrients to supply all that the plants need. So, we dose the water column to keep them growing. This process works somewhat different from lower light tanks. But, the effect of iron in the water, with intense lighting causing iron photoreduction, should be the same. I can't reconcile that with Ms Walstad's theory, knowing that many people do have high light, CO2 dosed tanks with iron being dosed in the water, and which don't have serious algae problems. But, there has to be a way to explain it. Similarly, why does a heavily planted tank discourage algae growth? It cannot just be magic. The physical reactions, and the science behind them, should be consistent whatever light intensity or fertilizing method or substrate we use.

 

[mistergreen]

We can go with allelopathy or simple oxidation to ward off algae off the plants. Oxidation on algae and iron. It looks like the iron oxidizes at night and photoreduce during the photoperiod.


I see BBA grow on hardscape but not healthy plants.

 

[Maryland Guppy]

Healthy plants are a key ingredient.

Allelopathy could be @ play.
Don't think it's ever been fully proven though.

 

[hoppycalif]

We can go with allelopathy or simple oxidation to ward off algae off the plants. Oxidation on algae and iron. It looks like the iron oxidizes at night and photoreduce during the photoperiod.

I see BBA grow on hardscape but not healthy plants.

I haven't been keeping up on aquatic plant allelopathy. Are there any new developments in that field? The last word I had on it was the problem that no one has been able to find the specific chemical or chemicals that plants produce to ward off algae. Such chemicals should be easily removed from tank water with activated carbon, and that should result in increased algae problems, but no one seems to have found this to happen.

https://www.plantedtank.net/forums/...eters/1006530-allelopathy-aquatic-plants.html

 

[mistergreen]

I don't know much on the field of allelopathy. I have a feeling the allelopathy effects are locally on leaves and not much else. I guess that oxygen produced locally would oxidize anything on the leaves too.

 

[hoppycalif]

When Tom Barr said that it costs far too much money to identify a complex compound for industry to invest in allelopathic compounds as algae preventers, that answers the question about why no one has identified any allelopathic compounds. Industry only invests big money when there is a big market, and our hobby is not a big market.

The best argument for allelopathy is, I think, the fact that algae rarely bothers actively growing, new leaf surfaces. That would seem to be the parts of plants that would be supplying the allelopathic compounds. So, if we see allelophathy as a protection that is part of the surface of growing plants, and not something that is secreted into the water, then there is a very good argument that it exists in aquatic plants and does protect plants from algae. That would also be why activated charcoal cannot remove it.

But, that also means we can only make use of allelopathy by keeping lots of healthy, actively growing plants in our tanks. (Imagine that!!)

 

[mistergreen]

There's plenty of chemicals identified for terrestrial plants like leptospermone, mesotrione. I don't see why aquatic plants would reinvent the wheel.

https://en.wikipedia.org/wiki/Allelopathy

 

[hoppycalif]

There's plenty of chemicals identified for terrestrial plants like leptospermone, mesotrione. I don't see why aquatic plants would reinvent the wheel.

https://en.wikipedia.org/wiki/Allelopathy

The presence of water, water everywhere, would be why aquatic plants would need to reinvent allelopathy. Water dilutes everything, breaks apart many compounds into ions, and changes how plants "communicate". Unless allelopathic compounds are passed along through roots, into the substrate, or by physical contact, through leaves, they aren't likely to work.

This is just my opinion, of course, but it does fit what we see in our aquariums. (I think.)

The reason for my interest in iron as a way to limit algae is that algae have to pick up all of their nutrients from the water, unless they have relationship with aquatic plants like mistletoe has with trees, and BBA may have that relationship, then I don't see how iron isn't their limit. Iron, as cations, in water, in bioavailable form, isn't nearly as abundant as anions are, and I think it is accepted that a shortage of iron can limit algae. If so, we should be able to take advantage of that in our aquariums.

 

[mistergreen]

I think limiting iron will hurt plants too. I don't think it's viable to keep nutrients only in the substrate. It'll leach into the water column.

*****
We know that npt get algae too.

 

[hoppycalif]

Ms Walstad points out that soil particles tend to be negatively charged on their surface, and that tends to trap positively charged ions like iron and keep them out of the water. (I need to reread that part to make sure I got it right!)

Edit: I almost got it right! It is the decomposed organic matter, humus, which has the negative charges, which capture the cations and keep them out of the water. I think that means it is those humic particles, with cations attached, which are affected by intense light, which can cause releasing of the cations into the water.

What if we never dose micronutrients, which include iron, except after the photoperiod is over, so the tank remains relatively dark until the next day? I have always dosed my fertilizers with the lights on, usually at about the time I turn the lights on. A simple experiment would be to set up two identical tanks with identical dirt substrates, and the same complement of plants. Give each of them a daily light dose of iron, one after the photoperiod, and one during the photoperiod, and see if they have different algae problems.

 

[mistergreen]

People don't usually dose iron in NPT tanks do they?
We know they get algae too so I don't know.

 

[hoppycalif]

People don't usually dose iron in NPT tanks do they?
We know they get algae too so I don't know.

NPT does not include dosing the water with anything, as I understand it. But, this would not be a hard experiment to do, preferably with inert substrate, to eliminate some of the possible variables. I'm not able to perform this type of experiment or I would try it. It could be done with a long tank, like a 20L, with a water tight divider in the middle, so the exact same light would be used on both set-ups, same temperature, etc. It seems to me like an important thing to check. If I was in a housing situation that allowed me the time and room to do it I would.

EDIT: I have decided to do this experiment, using a 10 gallon tank, with a divider in the middle, as soon as I get settled on where I will live. I already have a stand for that size tank, and 10 gallon tanks are now selling for $15, so it isn't a very expensive thing to try. Lighting may cost a bit, but using a couple of screw in fluorescent bulbs in dome reflectors should be too costly either.