I am just starting on soil, been doing hydro for a while now. I wouldn't use lemon juice, it will decompose from fruit juice to alcohol etc, haven;t used it, heard of it though. My wife uses lemon to put blond in her hair....I would PH balance several gallons of water and use that to FLUSH your soil for about 7 days with nothing but this PH balanced water. Be sure to give a good dryout period in between each flush.
Also... You might try using a different potting soil. I swear by my long time 50/50 mix of Black Gold CocoBlend Waterhold and everyone's favorite CHEAP dirt... Hyponex from Scotts. I get great results using this soil mixture in pots.
Get yourself some ph up/down and the local shop or online. I find the phosphorus based to be more stable then nitrogen based.
Question... How are we checking for dryness? weight? dry to the 1st knuckle? 2nd?