What kind of water is important also. If you go for a certain brand name of bottled water check several sources on its consistency in regards to PH and dissolved substances. If there is hardly any Calcium, Magnesium, ect. like in Aquafina then you may need some sort of CalMag solution. When you ad Aquafina, Big Bud, Bud Candy, Two Part Sensi Bloom, B-52, and Calmag the PH is 4.0 or lower so you want to invest in a PH control kit and PPM reader.
Pot size, soil, and other factors can have something to do with it. But many growers argue on these factors and many have really good results. 5 gallon is pretty big, but it is was I usually use for my taller plants I plant to flower longer than usual.
When a leaf gets a little worse you can compare it better to the link the TF offered.
Soil suggestion, if dirt go with black gold due to its wetness properties. Fox Farm is good too but some say it is too strong, except Forest I believe. Anyway, invest in some Advanced Nutrients if you have the money or Fox Farm for a little less.