reservoir problems

Hey, does anyone use humbolt county GRAVITY flower hardner? i just added it to my reservoir, i'm 3 weeks from harvest, just like directions on bottle. my ph went up to 7.0 from 5.9...and the roots covered in something slimy...it looks like mucas. throughout the whole grow the ph never went up that much or that fast. and usually when i change nutrients it takes about 5-8 ml of ph down to lower it to the correct level, this time it took 20 ml to get it back to 6 my res. has 10 gallons of water in it. also the ppm's have been dropping slowly throughout the whole grow, today it dropped by about 100ppm with very little water evaporation. just wondering if anyone knows why... has anyone used gravity before and had this happen??