The best thing to do is make sure that you keep a mental picture of what the plant's look like,soif this happen's again you will know what the problem is straight away.I always keep notes but code them so only you know what they mean.Droopy leave's are normaly caused by the plant's been over watered,sometimes the top few ince will look dry try to go onto the weight of the pot rather on the top 3 ince been dry.By letting the soil dry out will not harm the plant's at all,if anything thiswill goin yr favour by causeing the root's tosearch out water but there will be none there tilly ou water,whenyou do re water the plant may droop again don't worry if it does it will be fine.Get your ph right if your are new to growing i would get some advanced veg and bloom,this will take all the hassle of phing and messing around with ppm'sit is all done for you.But let them dry out and perhaps make sure you are not running to hot and you should produce a good yeild...................tyke....................