What does a balanced tank really mean and how does it slow algae growth?

[CT_]

Supposedly a "balanced tank" minimizes algae growth, but what is balance and how does it work?

I get the impression that balanced conditions is defined by  "optimal growth conditions for your plants, but not algae."  But that doesn't really help me understand how to get there.  Plants grow optimally, I assume, when all nutrients are present in sufficient amounts to be utilized by the plant.  If all nutrients are present can't algae grow too?  Do algae need unusually high levels of some specific nutrients?  I've seen several of cory's videos and live chats mentioning this topic but I don't feel any actually address my question.  Or at least I don't understand if they are explaining it.

[Yanni]

I guess that a balanced tank means that you've been able to find the point in your tank when the plants are all growing really well but everything else is just fine as well. Usually, to achieve a "balanced" tank, you need a small amount of fish and lots of plants. You can check out Fish for Thought's tanks as he puts a very small amount of fish and lots of plants. 

[Kirsten]

From how I understand, a well-balanced tank in these regards means the right balance of nutrients, living plants, CO2, and light. A good balance of all of those elements create thriving plants that grow and snap up all the available nutrients before algae can take hold. It also helps if there are creatures that eat algae, so that even if you're out of whack while you're getting set up and your plants are still growing, the algae won't be able to choke out the plants.

[CT_]

So really it sounds to me like you want to balance things so that your tank is nutrient limited so that nutrients are unavailable to algae, rather than in abundance.  but also "balanced" in that there is not excess of one single nutrient that algae may favor more than plants?

[FriendlyLoach]

A balanced tank is where the lights, nutrients, and co2 are all at a level that optimizes plant growth, and makes it so algae cant grow. To get there start with a photoperiod of 6 hours and work up, and just keep tweaking things till you get what you want. 

[Streetwise]

We had a fun discussion about this:

 

[Brandy]

Check out @Irene's awesome video clearing this up.

 

[MickS77]

To me, "Balance" means minimal maintenance while achieving my goals for the tank. 

[CT_]

1 hour ago, FriendlyLoach said:

A balanced tank is where the lights, nutrients, and co2 are all at a level that optimizes plant growth, and makes it so algae cant grow

How does that work?  Why can plants grow but algae can't?

[FriendlyLoach]

I am not 100% sure, but if your plants are taking up all the nutrients, co2, and light then you should be good. Whenever there's too much or too little of something algae gets hold. So you just have to keep doing trial and error until you get it right. 

Edited February 24, 2021 by FriendlyLoach

[Oakenstein]

53 minutes ago, CT_ said:

How does that work?  Why can plants grow but algae can't?

Plants, at least the faster growing healthy ones, are more efficient at taking up nutrients than algae. They'll eat first, so to say?

[Hobbit]

2 minutes ago, Oakenstein said:

Plants, at least the faster growing healthy ones, are more efficient at taking up nutrients than algae. They'll eat first, so to say?

Unfortunately it’s not that simple. To get a more complete answer, I had to turn to the master, Diana Walstad.

Walstad has a whole section on this in her book, Ecology of the Planted Aquarium. The basic premise is that plants have certain advantages over algae, while algae also have certain advantages over plants. Depending on the conditions of a tank, it will favor one over the other. Here’s the brief outline:

Advantages of Algae over Plants:

1. Better adaptation to low light. (Algae can actually photosynthesize more efficiently at low light than plants!)
2. Algae have more pigments than plants with which to photosynthesize so they can use more of the light spectrum
3. Better adaptations to high pH and alkaline water
4. More efficient uptake of nutrients from the water (for at least some species of algae)
5. There are a ton of species of algae in our aquariums that are specialized for lots of different conditions, while there are only a few plants. And since they reproduce quickly, whatever ends up being well adapted for our tanks’ conditions can take advantage of it.

It seems like algae has a lot of advantages. However...

Advantages of Plants over Algae:

1. Plants can get nutrients from the substrate (if they’re rooted)
2. Plants have large biomass compared to algae so they have lots of food reserves. (This is why you can starve out the algae without killing your plants by turning off your tank lights.)
3. Emergent plants get to take advantage of more light and CO2 than either submerged plants or algae
4. The big one... iron uptake. This one’s complicated and I’m not sure I understand it fully. But it sounds like (a) iron doesn’t build up in the water like other nutrients so it’s always a limiting factor for algae, (b) plants take up iron from the soil but will also slurp it out of the water regardless of whether they need it, storing extra for themselves and keeping the level in the tank constantly low, and (c) in the dark, iron binds other stuff in the tank so the algae can’t use it until the light comes back and frees up the iron again.
5. Lots of CO2 will kill algae but help plants (Not a natural process, just something we can do in our tanks)

This is getting long so I’m going to pause here and make another comment.

[Streetwise]

Lovely outline, @Hobbit!

[Hobbit]

Oh! I forgot part of it! Both plants and algae are (to varying degrees) allelopathic, meaning they secrete chemical signals that suppress the growth of other plants/algae. So if you have a lot of plants, together they produce enough anti-algae chemicals to reduce algae growth. It sounds like algae can also produce small amounts of anti-plant chemicals. So if you have a lot of algae, that’s no good for the plants! Plants can also suppress each other to some degree as well.

[CT_]

2 hours ago, Hobbit said:

Walstad has a whole section on this in her book, Ecology of the Planted Aquarium. The basic premise is that plants have certain advantages over algae, while algae also have certain advantages over plants. Depending on the conditions of a tank, it will favor one over the other. Here’s the brief outline:

Thanks for that!!  Looks like I've got some reading to do 🙂

[Oakenstein]

13 hours ago, CT_ said:

Thanks for that!!  Looks like I've got some reading to do 🙂

Yes very informative--more reading is what I did too! Now, I'm off to probably cause an algae bloom by experimenting with a longer photoperiod, but with with a light break for CO2 regeneration.

[Jungle Fan]

Here's another thing about iron I learnt:

if you add liquid iron, make sure not to run a UV-sterilizer because it messes with the liquid iron's chelation and renders it unusable for your plants. Some liquid iron fertilizers in Germany actually have this added as a warning to their products.

Just a little tidbit, that can have effect on plant growth.

[Brian]

I think people use the terms 

cycled - balanced - seasoned, interchangeable and this is a mistake.  
Make changes slowly, that applies to plants, fish..  everything.

observe your tank.  Watch the fish, look at your plants.  You should notice deficiencies.