How wet do you keep the soil? If not letting dry-out a bit, can cause root rot, and can look similar.

You'll need a bloom nutrient (fertilizer) lower in nitrogen, higher in phosphorous. There are plenty of three part fertilizer kits available. They are usually for Growth - Micronutes - Bloom. (one of the multi-part G-M-B nutrient systems, there's also 2 part, which come in an 'A' bottle, and a 'B' bottle.) Once you add the correct nutes, it should lower your water ph to within range.

Should try and find a small dedicated fan. Blowing fresh air across her helps strengthen stems, and provides vital fresh air.

Can you hold the back of your hand 10" below the light for a minute, without it getting too warm? I use a 400w, so don't know about 600's.