hey there Henvana, the burn marks on the sides of the leafs are from magnesium lockout and the burns on the tips are nutrient burns. This is not good my friend, you want to cut out all the nutrients and water with only plain water for at least 10 days maybe even 14 days. As long as your reduce the nutrients and feed with plain water with the plant should recover. Reading you i see "Plants are looking a bit healthier after flush though." keep that plain water coming , because the plants will like it lol. Hope this helps ! 🚀