Indoor - LED - Soil - BioBizz- Early problem

[kauptukas]

Hello fellow growers.
So started growing exactly 3 weeks ago (planted seeds to soil)
germinated well and everything used to be fine, but i noticed leaves dropping down and then turning to brown and crispy.
It looks like some deficiency, I watered 1/2 strength biobizz grow and added 1/1 recommended strength Sensi Cal Mag Xtra (2ml/) then phed solution to 6.3 and poured 300ml/each plant Top mid/top right mid right plants. This what I have taken so far. Plants are now watered second time, first time 1 week ago... i am pretty sure those are not over-watering symptoms cause leaves keeps dropping a bit each day, but started few days after watering for first time.
I'm using tap water, ppm around 300 ph 7.8-8.3. I let it sit for few days before using.
Soil is self-made with ~35% bio-humus, 30% peat and %35 vermiculite with perlite) first time trying mixing on my own.
Pots are carefully cleaned after each grow and reused, 12 liters each, buckets around 15.
Any suggestions, questions or chats below

Images:

P.S those are fungus-gnats whose are from soil and I hope to get rid of them soon.

 

[closetcasecfl]

Hard to see but little dots usually means a Calcium
Plants lacking Calcium balance can result in the soil becoming too acidic. Calcium deficiency can be fixed by foliar feeding (adding liquid fertilizer directly to plant leaves) one teaspoon of dolomite lime per quart of water until the plant's condition approves.

 

[fanleaf]

Over watering is definitely part of the problem. When stems are still up and the leafs are sagging it's too wet. Overwatering will cause all sorts of problems with pH and cause root and leaf problems.