Thanks for you reply anita.

Looking at my other red maple today I saw it has different symptoms, new leaves are coming black already and new developed leaves started to get dark and wilthered on the edge, practically in all new leaves this has been happening. Could this be anthracnose? I'm planning to remove all sick leaves, apply copper fungicide or difenoconazole, but I'm not sure if this would help.

Just checking. How much sunlight has this maple tree been receiving. Full-sun is 6 plus hours. 

from 7am to 4pm.

Questions: How long has the maple tree been in that pot? How is the air circulation around the tree? How do you water, and when? Any other facts please let me know. Like to see the entire area where it is growing, along with the entire plant/pot. Any other details would be appreciated on how you been taking care of your tree.

Anita

Sure
I bought it in February of last year then I planted it in a container but the soil wasn't that good to be honest. It soon lost wastheir leaves, fall then winter (March to August in Brazil) when they started growing again in spring of last year the same symptoms started to appear, I thought it could be the sun on the container making it too hot so I put it in a place where the sun didn't hit the container, just the top of the tree, but the problem didn't stop and the problem went all summer long, then fall of this year arrived and it lost its terrible sick leaves. In July I decided to change the container, so I put the red maple in a bigger one with a very good soil mix, when I removed it from the old container I was shocked because the root system hadn't developed at all in a year and a half (i will post a picture of its root system in july). So I planted it in a bigger container with a mix of sand, organic matter and dark land, the water drains really well, I water it when the surface of the container starts to get dry, now that rains a lot I don't even need to water it.
So Spring arrived and it had a few blossom then the leaves started growing but in a few days I started seeing the same problem, now even the older leaves are getting dark and wilthered on the edges some all over it.
No damage at the trunk. After this happens the new tiny leaves stop growing, causing the tree to get not developed.
Today I noticed some leaves completely withered, and dry I also tested the pH today it is 3,5 too low for a maple right?
Nowadays the container is between the hydrangeas where the sun doesn't hit it, just the leaves from 7pm to 4pm, I also have a silver maple in a container but the silver maple is  insanely  and growing super well
I am sending more pictures, it is still a very small tree
PS the white spots are sulfur that I applied

Thanks a lot

Now the root system when I replanted it in July, after a year and a half planted it barely had roots 

And the place where I am keeping it since July, the hydrangeas protects the container from direct sunlight, it is located in the middle, on the left it is the silver maple big and growing like crazy and on the right a trident maple, also growing well

The pH is very low. Soil pH is a measurement of the alkalinity or acidity of soil and is measured on a scale of 1-14, with 7 as the neutral mark. Any measurement below 7 indicates acid soil conditions, and anything above 7 indicates alkaline.