Help with the brown spot problem

First timer...
Leaves start out good then get the brownish spots. DWC grow using Foxfarm Big Grow and trying 1 tsp and then 2 tsp per gallon in a 9 gallon container. I have tried adding a little epsom salts also. Im also using distilled water to keep pH down. Pictures follow

OK here are the pics...

in your res. do you have alot of air stones spread out? the more the better and when you added the mag(epson) did you heat some water then add the mag stir till dissolved then add to the res? cause it wont dissolve right away if you don't ,and whats the ph of the water? get it to 5.8 or 6

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read this this helped me out a lot
it shows you all the signs and what they are caused by and how to fix
like i said helped me identify real early to fix probs at beginnings

OpenDNS
i have two small airstones that i keep fairly close to the roots, i was planning on adding more as I saw more roots. I did not dissolve the epsom salts before adding so I will try that next time. The pH is 6.0 - 6.2.

Koabear
I will give that a read.

Thanks for the help.

ok you need "large air stones" and a 'large " air pump more air will stop the micobial bacteria (pythium) from being able to setup on the roots,and tap water is a big factor in pythium unless filtered.(9 GALLONS!) if you dont have a reverse osmosis filter at least get a pur pitcher filter 9 gallons wont take long to filter and keep a tote with the lid on it and some "large air stones" and start filtering your water and that way you have a fresh supply of water on hand and then set that ph to 5.8 p.s. 2 small air stones wont do you need bigger you want to look in and see nothing but bubbles.

Surculus,
Thanks for your help. I'll get more air asap. I have a big res because i thought i would have 2 going at the same time. But for now i'm learning the ropes. Do you have suggestions as for the amount of Foxfarm to use per gallon and also the epsom. I am currently using 1 to 2 teaspoons/gal of Foxfarm.

if their young use half strength get a tds meter makes it real ez to start low and slowly push that level up a meter and tds pin is priceless to have on hand will keep you from playing a guessing game