improvement at blindfold chess

Hello everyone! I’ve been trying to improve at blindfold chess. I played against my dad up to two blindfold games at a time and I also played a lot of blindfold online. (Mainly on another site using the speech option and move input, looking at my keyboard only). And I’ve noticed that I have a problem with diagonals. Like the long diagonals and the diagonals where the bishops develop usually are ok, but the rest is confusing. I always have to count square by square which takes up a lot of time. I also have a problem visualizing the board as a whole. Now I found some techniques to visualize the board partly, like chunking the board into 4x4 boards or chunking the board into 3 parts: a,b,c files; e and d files; and f,g and h files, but it also takes up a lot of time... and the last thing is memory. Especially at the beginning of the game I feel like I have to go through the entire game from the beginning for the first 15-20 moves. Then I chose a position I memorize and repeat from then on. It also takes a lot of time!
Can someone help me out please!?

There's no easy road with this one max. But I can recommend a way to kill two birds with one stone.

You need to study openings. But rather than staring at the screen the whole time, work out the variations in your mind. This will help you familiarize yourself with basic positions on the board and piece placement. Before you know it you'll remember exactly where light square bishops go and where they don't go. You won't exactly visualize the entire checkered board square for square, but you'll remember the squares where each color bishop goes.

For example:

If I say white plays Bg5, then I immediately know that's the famous pin-square, that's where white pins black's knight to the queen. White does this with the dark square bishop (queen's bishop), which means g5 is a dark square. From there it's easier to remember that f4, e3 and d2 are dark squares.

You probably know your square colors at your rating but thinking in terms of light and dark diagonals really helps. One useful way of thinking of a lot of important diagonals is how a queen may operate on it. E.g. the light b1-h7 diagonal with a Bc2 Qd3 battery is often deadly.

Thenext step would be to think geometrically, in terms of triangles. Being able to recognize diagonal + file/rank patterns quickly is very important. Think for instance of the common pattern in many openings when Black has played ...c6 against a d4 Bg5 e3. Now Qa5+ is a very common diagonal to check on, picking up the bishop.

Lastly, a lot of this comes with practice. You'll get there! Bonne chance

Nobody visualizes the entire board at the same time, even when they have full sight....  

Really - notice how you look at the board next time. Do you look at the entire thing all at once? No, your eye darts around to the different pieces. You don't focus on the entire board at once because that's not how the brain works. GMs also move their eyes up and down the board, sometimes they don't see a long range piece possibility because it's at the other side of the board just like a beginner... but of course in an extremely more complicated position. The point is that you don't have to see an entire 8x8 board at the same time and noone sees it like that. Interviews given by excellent blindfold players confirm this and go even further with almost none them saying they see a board like as if they were sighted, the most prevailing thing is that they just "know" it and they don't know how. Like how we know a bishop on c4 will hit f7, or a knight on e5 will hit c6. How do we know that stuff? I think just study of games helps in this kind of knowledge. So most productive way to improve at it might be to just study sighted chess and it could just come naturally. There's no really good player who couldn't also play blindfold with a little thought.   

You might consider having an empty board in front of you - it may take some of the romantic ideas out of doing it completely blindfold but is vastly easier. It's also how they conduct the supposed "blindfold" Amber tournaments today (and super gms still make the odd blunder). It's a lot easier because your brain has something to place the pieces on and can see the diagonals and knight squares instantly. On the other hand, you may still be training calculation abilities for a sighted game because you will always have a board to base your calculations when you are playing sighted, even if you are moving the pieces far out of their original positions - if you get my meaning.  

Thanks everyone!