HELP!!! Top leaves are becoming yellow.

They look like they were overwhelmed with bloom nutes she needs to recover also slowly introduce flower nutes and defoliation slowly . Take off anything more than 30 % damaged and water her so she can go back to getting her nutrients from clean soil

Ph range for soil is 6 to 6.8 at 5.4 to 5.6 your way to far out and will have locked out most macro and micro nutrients. You need to get that ph in range.

Lights are Mars Hydro x2 TSL 2000 (with 75%) for 120x120 tent. I am using soil. For watering I am using only Advanced Nutrients fertilizers with Grand Master level. Regarding PH its 5.4-5.6 all the time. I was don't same thing to my previous grows, but for now really don't know what the heck is happening.

What I see a lot is that someone will flip to 12/12 and then go full force on bloom nutes. Too much P and/or K will then lockout micronutrients which makes it look like a calmag deficiency starting. Just remember when you flip, your baby begins to transition. I let her go for the first week on veg nutes, then I go half veg, half bloom for the second week, and by the third week I go full bloom nutes. My guess is that you hit her too hard with the bloom nutes after flipping.

Have you been watering with nutrients every time. If so thats bad practice. Have you been getting a good amount of runoff when watering. If not thats bad practice. Have you been using the correct PH for your chosen medium. If not you guessed it thats bad practice. Have you been giving the correct NPK for the different stages of growth. So many variables that a couple of pictures can't really tell us. My guess is either lights or incorrect Ph and nitrogen toxicity and salt build up in the soil or coco whichever your running in.

What kind of light is it.

Light is around 60cm from plant. Lower top leaves are also yellow.

Could be one of many things. If you ran a diary along with your plants we could all help lots more. My guess is light is to close and burning shit out of the plant.