Slow/extended release fert in your soil is something you don't want. Usually they slowly burn the piss out of your plant.the reason i ask is i hear of so many people adding fertilizer but i used a 6 month slow release potting soil NPK is like .05 or something really low but its been about 3 months and the plant still look a pretty green and is doing very well
i see some people talk about adding 15 8 8 and all these high ferts when mine is doing well with such a low amount..
Good luck to yalucky maybe.. i have 9 plants 4 outdoors and 5 indoors all are in slow release and 7 are doing great 2 still alittle small so i added ferts to them and gona see what that does .. if it burns i know not to add if it helps good