the lower older fan leaves are curling and develop...

Hello bro ! So the 1st thing you are doing wrong is the PH, in soil you should have a level between 6 and 6.5 PH instead of 5.5 like I can see here. The second thing you should change is your light schedule for a photoperiodic strain no need to give them more than 18h of light , the 20h is more an Autoflower schedule. The others parameters looks good to me except the distance from the light because even if you are using a led it is still producing heat so 12cm from the top is a bit low and you would cover a larger space with 20cm. Now about your leaves issue and from what I can see on the photo rhey are perfectly fine. Usually when you can spot a deficiency from the bottom to the top it is a mobile nutrient one and what you describe makes me think of a Potassium excess with your older leaves curling, with spots on it and that excess lead to immobile nutrient deficiencies such as Zinc and Iron and also a cal mag red due to the excess , you should flush your medium and low your Potassium amount, a flush can help to wash the nutrient excess away and make the balance .I hope it will help you 😁👍