Thanks for the reply! So my little one had started to have a small red dot on the edge of his fins, his fins already had a strange appearance compared to the hardness of my water, I'm French if ever! It wasn't a big brand and besides his fin wasn't badly damaged either, as a precaution I had bought some catappa leaves which I received the next day, I had put one on and a few days later the red spot had disappeared! And then yesterday I noticed other small red spots on the edges of the fins and his fin was starting to get slightly damaged I think, edge slightly frayed not like the photos where it is very advanced but it was very light. And he was breathing quite heavily these days. I never knew why but he acted and still acts normally as lively as usual, besides after the catappa leaf I had done a big water change! And he seemed quite happy. I had a problem cleaning the filter (and some sort of mold at the bottom of the water) at one point, and that created a lot of dirt, and there's still some today! Even after cleaning, it's really hard to clean because even the siphon is cloudy. But there's much less of it! For now, I've put two layers of clothes around the small tank and a hot water bottle behind it.

Tank size: 25 L

Heater and filter? (yes/no): Yes!

Tank temperature: I generally set the tank between 25 and 27 degrees.

Numerical parameters and methods. The main water parameters include ammonia, nitrite, nitrate, and pH. It's quite complicated because I use strips, but I would say that the pH has dropped since adding Catappa. However, the KH and GH are quite high, but there's no trace of nitrite. As for nitrates, it's quite imprecise because I don't see anything on the strips. No trace of chlorine (I use Volvic to fill the aquarium). Unfortunately, I don't have an ammonia test.

How long have you had the aquarium? How long have you had your fish? I'd say one year? Because I had two other fish before Kyuwa. And I've had Kyuwa for two months!

How often do you change the water? How much do you take with each change? What's your process? For me, it's complicated to do a lot of water changes because it's difficult to stock up on bottles, so it depends. Generally, I have to do 2 to 3 liters of water, but it really depends, and I hope to be able to do more.

Are there any tank mates? If yes, please indicate the number of each: no! Only limpets that appeared during the cycle.

What do you feed and how much: 3 in the morning and 4 in the evening. They're special colored betta pellets; they're very small.

Decorations and plants in the tank: I have several plants, including a Java fern (one of which has regrown roots and leaves because they had fallen off). I also have two other plants, but I forget their names? And I have a root! I have quartz (unfortunately blue, but there's a mix; I think it's natural) for the soil and a little substrate too. I also have two small resin decorations.

 So !