ok, first you need to get the meter, because even using half can still be problem if the strain don't like it....
Either way you are going to have to remove water and replace it with lower nutes... I would wait until you got the pen to do anything, because you need to know a starting point of what your EC/ppms are now, that way you can go lower from that value.
we need to know what EC it is.... make sure you calibrate it first before using it.
If it's a calibration one that is.....
What date was when you changed the water/nutrient mix with the pH at 6....?
You also must get a pH pen, the 2 most important items are a pH pen and a ppm/ec meter, without them, you must go by what your plants are telling you and even this can be difficult when you need to top off and add more nutes, because you don't know how much is in there and or how much needs to be replaced......
Hi again and thanks for the help.
I went and diluted the nutrient mix to 1/4 of the lucas formula on friday and didn't see the plants again till today. They had drank around 3,5 litres and the ph (which was about at 6 on friday) had dropped to below 4 (that's the limit of the drop tester). Does this tell anything? I added more water to the tank.
Haven't got the EC meter yet, hope to get it by the end of the week.
The symptoms have continueed, here's some new pictures.