[gabi.loraine]

Hi! This question is for @dwalstad but if anyone else has input of course it is welcome.

At my LFS, the bettas are in little cups with a little leaf that makes the water yellow/brown. I asked about it and was told it is an “almond leaf” which is an antibacterial which is good for the fish but also good against algae because “algae is a bacteria”. I was like ok give me some of those leafs, haha… This is El Natural, after all.
But now of course I’m second-guessing and can’t find anything about “almond leaf” in The Book, I’m honestly a little confused about the difference between algaes and cyanobacteria and the helpful bacteria that I might have killed by introducing the leaf… the snails are not particularily interested in the leaf, which is noteworthy … and there aren’t very many questions in this post but please give me your thoughts.
I’ll post photos of the leaves in the next comment. It is important to note that there might be a language barrier and “almond leaf” might be something completely different. The LFS is Chinese, and we communicate in Spanish, and I’m writing here in English. The Chinese lady at the LFS usually gives me the scientific names of plants in broken Spanish and I can figure it out, but this time she just said almond leaf.

 

[gabi.loraine]

 

[mistergreen]

A common name is catappa almond leaf, Terminalia catappa. You might find the tree in your area since they're introduced everywhere warm. Some other tannins can be used too like banana leaves. Most fruit tree leaves will work. Stay away from poisonous leaves.

Algae is a general term with many, many families, not just cyano.

 

[dwalstad]

Depending on concentration, tannins may kill or inhibit all bacteria and all micro-algae (green-water).
In the little Betta bowls, the leaves--via their tannins-- probably provide some protection for the fish. I doubt there is much nitrification in these bowls since there's not enough water circulation or surface area to stimulate the growth of nitrifying bacteria. The colonization of nitrifying bacteria takes time.
Blue-green algae is a bacterium that can photosynthesize. Other algae are just "algae." Please understand that my book is not a good place to learn taxonomy or get definitions. (Wikipedia is much more suitable.)
Tannins are astringent and bitter. They inhibit bacteria and algae. No wonder snails don't like them!

 

[Gooblikon]

Tannins also come from virtually all foliage and wood, Almond leaves aren't the only source for tannins which is helpful in replicating murky natural habitats. Scrounge up a piece of wood, clean it off, and bake it for sterilization. Although boiling it might be better so it absorbs water and is more likely to sink instead; do this later in the day so the tannins build-up over night and you can pull it out during the next day if you see it becoming too dark.

 

[gabi.loraine]

Tannins also come from virtually all foliage and wood, Almond leaves aren't the only source for tannins which is helpful in replicating murky natural habitats. Scrounge up a piece of wood, clean it off, and bake it for sterilization. Although boiling it might be better so it absorbs water and is more likely to sink instead; do this later in the day so the tannins build-up over night and you can pull it out during the next day if you see it becoming too dark.

Oh I did that. Then everyone told me to get rid of the wood to get rid of the algae infestation I had, which finally subsided when I did listen and remove it.
This thread from last year.

 

[Gooblikon]

Oh I did that. Then everyone told me to get rid of the wood to get rid of the algae infestation I had, which finally subsided when I did listen and remove it.
This thread from last year.

Leaves are still a choice and so are certain teas. As for bark if it's been boiled or baked it shouldn't be an issue as far as I know. Regardless, the solo betta tank makes it more difficult to have a cleaning crew to maintain the system.

 

[dwalstad]

Then everyone told me to get rid of the wood to get rid of the algae infestation I had, which finally subsided when I did listen and remove it.

I don't see any need for tannins in an aquarium. A tiny bowl in the store, perhaps; in a typical planted tank, no.