First LST grow

Can I top the main stem of the plant?

freebie seed from herbie seeds heavyweight fast and vast auto
Pics with flash and led on they look like candy lol

I ended up toping plant and this is how it looks now. No I have a quick question so I feed my plants 188 ppm of fox farm nutirents and the tips of the leafs just started to burn. So next feeding should I feed a little less nutirents like 150ppm or keep feeding the 188ppm of fox farm nutrients?

Tips started to burn.

My vast and fast are ready and hanging can't wait to try them.