A few things to remember with regard to growing indoors that are often neglected to mention.
You have used a mulch, light won't evaporate top couple inches of soil. With plastic pots, meaning 0% of the water will evaporate from medium above 50%RH especially so with plastic pots and mulch.
Plant is dependent on transpiration to remove water from pot, when evaporation is low or non existent and transpiration is crippled or slow this could very quickly leave the medium oversaturated, but that's something you should be able to notice visiting the tent daily. Also to note, transpiration itself is responsible for nutrient uptake so if it's slow, alot of the salts your feeding your medium will just sit in the medium building up EC in medium.
Transpiration is a daytime only process, which draws moisture from soil and pulls it up using cohesive force of suction. At night no water leaves medium it sits and stagnates. Soil aeration is crucial for phosphorous uptake, upto 51% of phosphorous in a plant is uptaken early hours of nightfall (given conditions ofc)
Water is a transport fluid, a solvent. If it's going in at 6.16 and coming out at 7.62 it means as the water is passing through medium picking up excess salts, with no where to attach its just leeching out the bottom. If your pH is going up, there is a over abundance of the big 3 cation, Ca, Mg, K. Micro-nutrient uptake is effected above a pH of 7, symptom normally present as a lime-greening of leaf all over with no obvious starting point, similar to what I see in your pictures.
There are 2 methods of taking EC readings, you can take a EC from water which will read total dissolved solids in form of ppm.
There is also a soil EC metre this will give you a EC reading for the medium. This should generally sit around 0.5-1.8, never higher than 2.0 and is measured in ms/cm or us/cm. Basically micro and milli. units or whatever. There are conversions you can use for ppm to us/cm, to make it simple but I forget exactly what they are. Easy to find if needed.
You should dilute your medium to reduce the salt content, reapply desired ph'd water once EC level return to range. Then apply a balanced fertilizer suited to stage of growth. Keeping tabs on ec and ph periodically.