Hi, answer to your mixing yes its possible, and adjusting with lemaon juice is possible but sometimes you need some basic stuff to change ph ( if its to sour for example. But i wont worry so much about ph atm.. as you are growing in soil, it not that big problem, Soil buffers the PH very well, if your soilmix is well balanced. To me it looks like a premixed Soil so i dont worry at all. Ok now back to the nutes...No need to feed them atm, They are small and sitting in prefertilised soil. The soil can feed her much longer. I personally dont use any Vegetation Nutrient on automatics... sometimes only if they stretch heavy and show defiencys....so lean back give them water and beneficals like calcium , magnesium molasses , humic acid. Thats pretty enough until the y reach the point of showing defiencys ( older leaves getting Yellow). If ou want you can look into my Diary " cookies for me" there ive listed a nice benefical drink for the girls... Happy growing. Greetings to Argentina
p.s if you mix nutes , take the water, mix in nuts then get the ph of the mix, and always give nutes into wet soil