Can you help me

Looks good for day 21. what i see is potentially a bad waterign habit.. only a small diameter around the plant looks like it get watererd. always water entire volume and allow the plant to drink it down. if you water teh top and don't water the whole thing, you promote superficial rotos... or you simply don't make use of the areas that are constantly dried out -- not only that the zone between the dry and the wet will be a risk of building up dangerous levels of nutrients. that ebb and flow keeps leaving minerals behidn that add to the next bit of moisture that comes.. and adds up over time. always water entire volume. always allow the plant to drink it down and repeat. don't micromanage or over-think it. 20/4 is fine, but if you can provide 35-40 dli over 18, it's not a good idea.. the hours of operation should only be longer than 18h if you have a weak light. read up on Daily Light Integral. use umol/s produced by light on spec sheet divided by your area in meters-squared.. then reference a DLI table with that number (ppfd) and hours of operation to guesstimate your DLI. Many variables are at play, so this is just a small ballpark to start and you need to observe and react to plant growth to further refine it. length of internodes is great way to assess light intensity.. too tight, need less... too stretchy, need more.