you need a ph test kit for your resv. try to keep it around 6.5 lemon juice is a ph downer not an upper you can use bakeing soda for an uper but you can get ph up and ph down for about $10 at a hydroponic store or go online or ebay its a lot better for your resv. then just dumping lemon juice and bake soda in your resv. depending on what type of system your useing you might need a p.p m meter also! you need to go to the hydoponic forum they can give you vital infomation that you need! good luck bro