try putting something over your soil to reduce the dying time and need for regular waterings, trace out the pot base on some cardboard/plastic/mylar and cut it out, then make a slice half way down the middle and put a hole for the stem to fit through. Also yellow leaves are SOOOO hard to pin point but my guesses and again these are only guesses with the information provided are..
Lack of light to the lower leaves, the top leaves look beautiful
Bad soil PH, i noticed u said 6.5 is that the soils ph? if so u sould be right there if also watering with 6.5
Nute def, mainly nitrogren but im doubting this one due to the darkness of your top leaves.
But really i think it just comes down to, too much heat and too many waterings.
