Get an EC probe.
Keep it between 500-900 ppm. If it is hot, go for the low end of the range.
>bro this is my first grow. But it seems
add 1 tsp of vinegar per gallon of water, this gives a relatively more accurate ph to start with if you don't have a ph meter (you NEED one Soil and Water PH meters, PPM meter - amazon), it does look to be a potassium or a phosphorus deficiency, but i do think its from the ph.