4ml of AnB is way too much run the pots through wuith lots of water like Beefy says at least x 2 to pot size more like x 3, sling run off away that comes out and start back up feeding asap with 2ml per liter you shouldn`t have to go over 2.5ml a liter the whiole grow as well, 4 ml per liter is way too much.
It`s hard to tell but i can just make out those darker shaded brownish edges and burnt looking look from overferting. NAot that pictures are called for when you saying your adding 4ml per liter we know its overfertigation (loving that word lots, that`s if it is a word) woes and ways

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Silicon yes i suppose ive read add it first and last Minty, myself i just add it first and sling in AnB then ph it back down and have done for years now, i did used to add it last but i find its easier to bring ferts back together ( milky looking ferts seperating not mixing right caused by Si) with ph- later after adding AnB, jobs a good en. :)