Potting mix might be too cold and damp.

Like embothrium said could be soil temp and damp. Next thing would be lights and what kind of air circulation it's has

Thank you for your answers. The usual temperature here is around 80F and we only add some water (never overflow) after the mix feels a little dry, my house has good air circulation.

I wanted to ask, I heard once that loud noises (music, tv and such) can stress plants, is this true? My father has lately been watching tv at an exaggerated volume (you can still hear the tv loud and clear outside of the house).

Again, thank you for taking your time.

lack of light.. almost all fruit trees are full sun ... you house isnt ...

noise means nothing .. imo

ken

Yes, lack of light. Plants run on sunlight, you know. A plant adapted to full-sun conditions sitting in a dark corner in a house somewhere isn't getting any energy input. You might think it's a bright spot but if you took a light meter where that plant is sitting and compared it to even a shaded area outside, the outside location would check out much brighter. It's dark in houses!

You don't give much information about where it is sitting right now. Have you recently moved it? It needs a sunny window and even watering. Not too much; not too little.

.........yes, and even that sunny window will be "dark" compared to the great outdoors. Mangoes, as well as nearly all fruit trees are creatures of the sun. Nobody in the whole world is growing fruit trees-for production-inside of houses! So as a house plant experiment, your tree may go on for a while, but if this is a serious effort at having a producing mango tree, you need to be working outside. Where the sun is.

Noise doesn't effect plants in a harmful way only difference you'll see in some plants is growth from vibrations. If noise effected plants all mine would be dead i love loud music.

when growing indoors where you put disease at a very low limit of attacking your plant and you see foliage drop and it's black where it was connected to the plant running down the veins clear sign you shaded your plant an it no lower wants those leaves so it turns them off.

the black you see if the inside rotting

Thank you for all the comments, very appreciated. This wasn't a bought tree, we actually germinated the seed, that's the main reason why it was indoors, also, because we live in a very heated city (surpassing 120F during summer) and it's also very dry, just a small hand full of plants can actually survive full sunlight here, Since it was so small we were afraid the sun and heat would kill it so we thought of keeping it indoors until summer ended.

Lately the temperature's been nice (around 95F max) so I guess it's time to finally take it outside :) Thank you for your advice! To those who asked me about recently moving it, the sapling has always been next to a window but since it has grown a lot during the past weeks I guess now it need more sun power, hehe.

Try to water only when slightly dry. That said, even temps in 90s sound hot to me, so don't get careless the other way and skip a crucial watering. A potted plant has that pot as its whole universe.

Good luck!

It will surely burn if you place it outdoors in full sun without some kind of shading. I mean it will fry and drop all leaves. I think you can probably keep it alive indoors near a sunny window. No, it will not thrive, but should live. I've started many of these in my life. But, like all trees, they soon outgrow your indoor space, unless you have a conservatory.

Yes, adapt to sunlight slowly. forgot to mention.

Even with a shade cover it would burn..always been in cool ac with very little sunlight. Best to put it by a window with a blind closed an slowing let the tree meet the sun