Mushroom In Indoor Growing Soil, Along With Other Issues...Pics

I found a 1/2 inch white/tan mushroom in my soil. I messed it up when i took it out but it reall didnt seem to be attatched to anything? I scavenged through the pot and didnt see anything else. I know i have been overwatering my plants and am in the process of fixing the problem...i have to let them dry out. It also looks like their are roots coming out or attempting to come out of two of my pots drain holes. The one with the mr found in it is a little over 10 inches, and the other one is right at 8. I should also say ive been pretty good at emptying the water runoff after i do water, but the plant with the mr i must have missed bc their was still water in the bottom after 2 days? I just dont kow anymore. I want to transplant in better soil but scared to mess my plants up. ive stunted them to the point that its been about 9 weeks and my biggest plant is 10 inches tall....ithe dont look dead by any means i just need someone to point me in the right direction. I also have what looks to be salt crystals in all of the pots? And they def. need some mag....i have picked up epsom salt i just have to wait till they can be watere. Ph of runoff is a little below 7, and temps are between 84-86. 400w hps indoor soil grow. Miracle grow all purpose plant food for nutes 12-8-4. Ive only fed 2 times at less than a 1/4 strenght. I also have ben supl. superthrive at 1ml per 2 gallons...1/2 the recomended dose. Please help

bump...any help would be greatly appreciated

when they are that young they really don't need any nutrients the soil should have plenty in them already

The soil i purchased didnt have any nutrient info on it....So these plants are 2 small to be feeding than? Any thoughts on the mushroom?

never tried mushrooms compost buddy next time try foxfarm soil or happy frog soil can't go wrong with that stuff

Never used the stuff. My plants arent even 9 weeks old. I just looked back when i bought my hps and that was the 26th of last month. so they have only bee under the hps for almost 2 1/2 weeks. The were brought up under 2 40w fluros i use in my garage. I really wish i would of wrote this stuff down. So my plants are maybe 5 5 1/2 weeks of age. I read somewhere that when they develope their first 2 true set of fan leaves to start nutrients. If this isnt true than when should i start? Some help a brotha out lol. Im really stressing