yellow/brown lower leaves

Hey guys im on my first solo grow (i've helped friend/family on grows before) and i've got a problem. i've a 3 plants(2 auto's and a lemon skunk) in a DWC. the auto's have been flowering about 2-3 weeks and some of the lower leaves are starting to get yellow/brown spots which start to cover the leaf. it started with the lowest leaves that were covered by upper foliage and didn't much light. now it's started on leaves getting a full blast of light.

light - 400W HPS 13" away
DWC solution - pH'd water + ionic bloom + H2O2 pH 5.5-6 EC 1.6
temps - 25C light 18C dark
RH - 40-50%

pic below and all help much appreciated

Looks like a serious difficiency, flush of any excess salt buildup, perhaps double check your nute solution and address what it may be lacking. Also check that your res temps aren't anywhere above 75F

What type of water are you using?

i dunno about build up. i may have something to do with changing nutes from grow to bloom. But its the same brand hydro nutes so that shouldn't cause any problems i don't think.

i was using tap water at the start. i now use distilled water.

did you have problems when using tap water or did it start when you introduced the distilled water?

flush it out and check your ferts. dont know much about hydro but i would think that the plants still need all the same nutrients.

Waaay too much N at the very least dark green and "gangly/fleshy". ... I suspect nutrient toxicity/lockout. EC of 1.6 is very high imo ... try going to EC 1.0 ... cn

it's been a few weeks since i changed to distilled. This started 7 days ago. i was thinking cal/mag deficiency as they could have had a build up from the tap water so it's only showing now. the tap water pH started at 7.5-8

i might calm down on the nutes at the next change but i've been ramping them up at each change and haven't seen nute burn yet.

Also the lemon skunk vegging in the exact same setup is looking lovely i can post pics if you want.

Looks like classic magneseum deficiency.
! teaspoon of epsom salts to ea gallon of water.

Google mag deficiency images for cannabis. Looks like it to me but could be wrong.

I agree jumpin, from google images it definitely looks like mag deficiency. And that might explain the timing.

Are epsom salts safe for a DWC or should i get that calmag+ i've seen around the forum.

Epson salt will do great foliar feed for a faster result but make sure you disolve in boiling water first. Treat for about 2 weeks every other day should all clear up. i would spray with ph'd water between treating to get rid of any dried salts on the leaves.

If you are using distilled water there are no disolved minerals. unlike tap water that has alot of calcium and magnesium + over 20 other crap that comes out your tap. distilled doesnt its best to cover yourself.

Thanks Godspeed. i had imagined this happening when the water changed but i thought it would show up by the 2nd res change with the distilled. And my nutes say they contain both magnesium and calcium. The company(Growth Technology) advise adding silicon but not cal/mag.

anyway i'll try this. and get back to ya.