Trainwreck not growing well, need advice

Growing experience: 1st time.
Using 150W HQI at 20cm of distance to grow.
Soil has peat moss(imported from Holand), coconut soil, (trying to get a 5.5-6.4 range of PH),and it has some sand and other normal stuff but not humus.
Water: Using a distilled water (ph at 6.2) filtered by machine
AGE: one is 60days. The other is 30 days.
Problems:Lower Leaves getting yellow and tips of leaves getting dark.
Ph meter: has a shitty one, trying to buy another imported one from Japan used for soil (hope to uderstand more about the ph of my soil)
Fertilizer: imported natural vege grow from japan. (a bit expansive but still testing it's strength)
Presently trying to make some home made humus using leaves, leftover and hoping it will contain.

Questions: What's problem with my plant? Need advice.