might also want to see how much nitrogen your given them
check the back of the nutes u have use and the dirt and that will tell ur there nitrogen content

the reason i say nitrogen is because thats what alot of plants are suffering from when just the bottom leaves start turning yellow
thats is the main problem i ever have with mine is nitrogen deficient

but the curling ross probably hit it on the head with the over watering

post up some pics and ur ph lvl when u get a chance