Directions Lagoon Blue

How long did you leave the dye on for?
Did you dilute the dye at all?
When you applied the dye, was your hair clean/dirty, wet/dry, conditioned/unconditioned?
What colour was your hair before you applied the dye?
What strength bleach did you use?

Hello, I bleached my hair using Schwarzkopf Blondme Premium Lift 9+ with a 20vol developer, twice. It got me to light blonde. Before applying dyes, I wet my hair and towel dried it. It is clean, slighty damp, unconditioned hair. I did diluted the dye 1:1 and leave it on for 6 hours, all wrap up in cling films.

Hmmmm.  OK.
Could be that diluting the dye is the problem, or it could be that your hair is too porous to hold dye well, after all the bleaching & processing it's had.

Try it again without diluting the dye?  and leave it on for as long as you can.  Some people leave it overnight.
Blue dye on yellow/blonde hair will tend to fade to green unfortunately.  You could try a more purple-based blue to counteract the green a bit.

Since it's a dip-dye, it's easier to avoid getting harsh shampoo on it - when you wash your hair normally, just apply shampoo to the scalp area then let the suds run over the lengths as you rinse.  You can also rinse the dipdye in colder water to help the dye stay in.  Try to wash your hair less often as well.

I wash my hair once a week, using shampoo on my scalp and letting it run through, then conditioning, then rinsing off with cool water.  After bleaching and an early attempt with diluted dye, I had a yucky greeny-yellow base.  I then applied a mix of purple-based blues and left it on all day.  My dipdye started off a fairly dark inky blue, faded to a mid-blue with slight green undertones after 2-3 weeks then stayed like that, gradually fading to a mermaidy blue-green after about 2 months.  It's green now because I'm deliberately fading out to try the next colour  😉

Thank you, I will try not diluting dye next.

I am wondering if not washing my hair using PH balance shampoo have effected this negatively. I'm finishing my shampoo and will purchase a ph balance one soon, however, I tried not to let my current shampoo get anywhere near my dip dye. Moreover, I did not notice any staining nor did the water look blue when I wash my hair (hardly any dye run when I rinse the first day either).

May I ask which blue dyes are you using, lagoon blue is pretty but I think it's too pastel and economically not so cheap so I am looking for a better thick blue dye I can dilute.

I mixed Directions Atlantic Blue and Neon Blue and a little of Adore Indigo Blue.

I have never had good results with Lagoon blue, it always comes out patchy and fades quickly for me. It definitely isn't pigmented enough to take a lot of diluting.
So I would try a different blue, Atlantic blue and Neon Blue are both great shades, Atlantic dilutes to a sky blue shade, it is quite turquoise, while neon blue is purple based so dilutes to a cornflower blue/lilac shade. You could add a dab of Neon to diluted Atlantic to get a shade similar to Lagoon.