Tips of your plants look kinda like burned, as i can see you are dripping water on your leaves. That is probably the reason for the tip burn.
Gnats are anoying for sure. I haven’t had a big problem with them. I am using
biobizz and plagron mixes. They are coming from your soil mix, if you are growing organic, the h2o2 would fuck up your microheard. You may want to try mulching or there are some good soil drenches which are suitable for organic farming. I think you can use BTI. Personally i drench the soil before first use with “Neemazal”. In the same principal
Azamax or any neem based pesticide could be used imho.
If you really want to be organic and minimalistic, add nothing till you see deficiencies. Then there are stage apropriate organic fertilizers you can top dress with.
For example, wormcastings, kelp, alfalfa, any rich matured compost with high N is good for veg and bat guano, banana peels, again kelp and anything with high P and later in the flowering high K is good.
They don’t look hungry to me and they are doing well it seems, congrats.
I think they would benefit from a little epsom salt spritz. A very gentle dose. I use 1/4 tsp per liter and go from there. Not necessary by the way. It seems some leaves have getting a lighter hue between leaves. Any case it will not hurt anything.
Also. How high up your each light is from the plants?