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I dont know much about ph issues so let someone else deal with that
Yes it miracle grow or any pre fert soil that bad my first I had leaves dieing and curling pretty much whole time. Switch to diffrent soil asap. Also that isnt a whole lot of light for flowering prolly gonna need some more.

 

I dont know much about the pool shit but it might be kinda strong. but youd think if the ph is good then the ph is good. hell i dont know, id get some actual ph down for a hydro set up ust to be sure that its somethong you can feed your ladies. maybe that pool shit is bad for your girls.
as for the miracle grow, i dont use it personaly but ive seen grows done with it and they seem fine to me. some people sware by the stuff. i guess its your own perogative. so the only thing left is maybe the time release part of the deal. ive never heard anything good about time release ferts. always some sort of burning. the shit is bad, is the point im trying to make here. no fucking time release shit people! stop using it. flush and do whatever you can to get ride of the shit.
good luck............

 

I would be wondering about the ph down you are using. But yes, MG soil does suck that hard. See its got these nute balls inside that pop every once in a while giving a lot of nutes all at once. nute burn is very very common with MG soil. Most people on here I see using it end up repotting into something else after a month or two when those nute sacs start relaeasing their stuff. Another thing is that MG is notorious for putting their stuff in all of their product. I was looking at a bag of MG perlite, and it even had been trated with nutes!

 

Ya that'd prolly work out alright. I am of the philosophy that pretty much any soil will do as long as it doesn't have nutes already in it like MG. I figure if hydro can work and people supply the plants with what they need succesfully (which a lot of people on GC do) then about any soil medium will work too. The most important factors are that air can get to root system (which you've taken care of perlite) and that it doesn't retain moisture too much (again perlite). What you got going on should be fine.