1st Experience

Hi bud . No topping is not necessary before LST . Infact as you are growing an auto I wouldnt top at all. I find it's best to LST as this means you can shorten the plant and get all the tops to an even level . Pretty much spreading the plant out instead of allowing it to grow tall. Giving you optimal light coverage Increasing yields. But each to their own, some People choose to just leave autos alone completely as they can stay short anyway . I'll be uploading a few pics this week of how I LST in the next few days 👍

Nitrogen. If it starts from the bottom working it's way up then it needs more Grow.

You have your ph as 7. That is too high. Go to around a 6.2 to 6.3 range. Plants love slightly acidic soil. Plus ph is needed for proper nutrition absorption. After looking at your dairy I see you are slightly nitrogen deficient by yellowing leaves at bottom. I would not cut back on feeding. Worst time when plant is producing. If anything, add more phosphorus and potassium. It needs slightly elevated levels during flowering to produce bigger and denser buds. When tips are yellow but not burnt and curled up it wants more potassium. If burnt and curled up it is nute burn. In your case it is wanting lower ph and more right now. Good luck. Hope that helps. Happy growing 🌲🌲🌲👊