GoGrow is totally on with this one...
Without proper potassium and phosphorus levels nitrogen won't get used... The plant is starving.
If it were to produce yellow edged leaves at the top of the plant, that's a nute burn.
The leaves near the bottom that are completely yellowed can be removed, they won't get better, and they have little to no chlorophyl left in them... They're useless and prohibit growth to the top.
From the looks of the pics, they're droopy like they're thirsty...
When you water, you wanna make sure you give them enough for some drainage out the bottom of the pot... Then wait until the pot is light before watering again.
Sticking your finger in it only tells you the surface moisture, it may be mud further down.
Lift the container to see if it needs watered, it'll be featherlight when it's ready for water... And heavy as hell after watering.
If this is too hard, you can get a moisture meter (probe) for like 5 bucks at wally-mart.
You'll want a good all around fertillizer with higher PK ratios for blooming... I'm not sure of what MG is the best, but my father used MG for acid loving plants (formerly Miracid) it's lable says 30-10-10 which is more for grow than bloom... If you can find one that's 10-10-10 it'll work, but a 5-10-15, is the best ratio (like gogrow said)