I don't know where you live, but go to an indoor grow shop and get soil they recommend, which will be something like Foxfarm's or Roots brand. Supernatural used to sell in these shops but I don't know if they still make a potting soil. I don't understand why you're being advised to flush as this will not solve your problem. You need better soil, not the flower store stuff you're using. While this stuff isn't bad, you have to add everything the plant need to survive, obviously, or you wouldn't be having this problem. It is a problem of nutrients, not water or root rot. Seldom will you see root rot unless there is alot of water and very high temperatures. You can continue using that soil if you want, but whether you get new soil or not, get a bottle of Dynagro 7-9-5 from an indoor grow/hydroponic shop and follow the directions on the back for a soil grow, 1/4 tsp to 1/2 tsp in a gallon of water, probably every time you water and in a couple weeks transplant to a bigger pot, preferably with foxfarm potting soil. Just don't water all the time, let the soil dry out some before you water again. It won't cause root rot to water, but roots need oxygen and the only way they get it in a soil grow is if you let the soil dry out between waterings.