if its at 4 weeks, most of the soil nutes would be used up by then unless you change the soil. i also notice that if the pot is too small for the strain, it will be harder to use the nutes. yes, yes, yes, first and foremost is to check the ph, if its off, they wont take in nutes, but with the same respect if you have been feeding the whole time with the ph off, nutes will build up in the pot as salts, you may notice hard soil with white on it. if this is the case, you gotta flush it out. if you plan on flowering soon, id transfer to a 5 gal bucket with new soil, but wait to add nutes till they adjust. this is the only time id ever use superthrive as it has caused bacteria in my hydro systems and smell god awful. it helps transplant but is extremely concentrated, i use three drops a gallon and it sometimes seems too much.