We watered them the same way farmers do, with two inches of water per day, until the water drains out the bottom, last week my grandpa sprayed the plants with a special soap to get rid of the bugs that were eating them, and over the past two weeks, the edges of the leafs of three of the plants were turning black, and now it's all four of them, and plus the leafs on three of them are turning yellow, We assume they may have a disease or something, so How do we get rid of this disease?