First grow purple lemonade

Starting this diary week 2 because I'm having some issues and this can be a very good way for me to learn since this is my first grow. So everything went well until 4 days ago. Since then my plants, mostly the amnesias, are developing yellow new foliage. Tomorrow is the day I am getting a ph meter, I suspect the problem lies there . I have used an Activozin phosphorus based (5/20/0) fertilizer that is good for root growth and transplanting. It's in the form of non degradable granules. I was watering 160ml tap water (silly me) over the seedlings every 2 days until mid week when I noticed soil was dead dry near the edges of the pots so I gave them 1lt to wet it a little. Today, after 3 days I gave them approx 700ml. I have a light mix soil mixed with 30% perlite. From my research it could be phosphorus toxicity, iron deficiency or sulfur deficiency. Or it could be over watering. Or it could be poor drainage. Or it could be light deficiency (I have a 42watt Tled with some led strips until Mars 600 arrives) If you haven't noticed I am kind of struggling. Let's have a happy bumpy ride 🙂