usually when leaves curl down it means lack of nutes, but it sounds like bugs too. check your ph again and check your plant with a magnifying glass closely, check every square centimeter, underside of leaves especially, caus alot of the mites or bugs like to hide there. if it`s bugs, you need to get some insecticidal soap and spraythe whole plant, undersides of leaves too. it`s biodegradable ant wont hurt your plant.
i hope this helps you , it sounds like you know quite a bit already.
it`s good to see a knowledgable grower on here
i have been growing about 20 years, indoor, and i`m still learning new things to help me.
good luck