Hi,
After decades of growing in the backyard garden,I decided to try an hydroponic garden indoors.
This is a "New Big Dwarf" plant. (I have grown it in soil with awesome success)
I use MasterBlend at 2.4 -2.4 -1.2 as recommended.
I have a RDWC system with 15 gallons.
As you can see from the pics, it looks like I have Mg deficiency but I have tried a foliar spray with epsom salt with no difference, I then decide to add more magnesium sulfate from MB (2.4 -2.4 -2) and still the symptom persist.
No pests.
Lowering and/or raising PH, no changes (Keeping at 6).

Any thoughts ??

I think that with the veining that it is an iron deficiency. I also think that with those brown spots on the undersides of your leaves that you are starting to get gray mold. Remove the leaves with the spots and use your favorite fungicide. Mine is daconil alternated with copper spray. Neem helps as does sometimes milk.

Are you monitoring your reservoir ph? Is it getting warm at all? Are your roots more brown than white? Without optimal conditions, roots will rot and that shows as nutrient deficiencies.

Welcome to the forum [mention]dirtdan[/mention] !
That could be another nutrient deficiency, not just one of the usual ones, unless all of those micro-nutrients are supplied.

@MissS, chelated Iron is on its way. This is an other deficiency I was looking at.
Will keep an eye out for mold.

@Cole_Robbie, PH and EC are monitored daily, everything normal. Temps are actually getting colder up here in Montreal (22c max in my basement)
Roots might be a few degrees colder.
Roots are silky white using bacterias "Southern Ag Garden Friendly Fungicide".

@pepperhead212, Thanks, I use MasterBlend, a 3 part tomato fertilizer so I'm hoping primary, secondary and micronutrients are well balanced but obviously something is a little off, hopefully the Iron will do.

By the way my cucumber plant is starting to show the same symptoms.

I don't grow fruited plants in my DW setups (one 27 gal and one 12 gal) - only herbs and greens. I never used Masterblend, but I have used 3 different brands, with no problems, as they always seem to get the micro nutrients the plants need. I add some Karma, and some silicate, when setting them up, plus some calcium nitrate - an idea I got from using it in my Earthboxes, plus, the greens and herbs benefit from the N. I add some potassium bicarbonate, when the pH goes down. I also keep a small powerhead with a sponge filter in each tub, not just an airstone, to help with the aeration - I had a bunch of things like this sitting around from old aquariums! The temperature is slightly lower than yours, but not much, but I don't know how high tomatoes should be. The white roots sound good. Hopefully, the iron will help. Otherwise, maybe something in the local water?

What lighting are you using?

@pepperhead212, local water should be fine at 0.11ec and getting a reverse osmosis system is something I'm hoping I won't need.
Most people on the net have great success with the MasterBlend tomato 3 part fertilizer so I'm a little confused.

@Cole_Robbie, I have the SolarXtreme 1000 by California Lighworks.
Keeping it at 600 µmol.

I think one of your micros is locking out another, or it could be too much nitrogen. Your grow system and equipment are top of the line. That could necessitate tinkering with the nutrients if your uptake of them is better than most home grows. I think you likely have too much of something rather than too little.

If it were me, I might try switching the nutrients out to a different brand like general hydroponics or fox farm just to see what happens. Masterblend works, you just have to get it dialed in for your conditions.

I'm curious, did you happen to order new nutrients recently? I seem to be having similar issues and I have a new batch of Masterblend. I have not seen these issues before.

This is the first time trying MasterBlend, I have another batch coming in so I'll see if that changes anything.
So far I have lowered N a bit, increased P, K and Mg a bit and this seems to be helping but I still have some minor yellowing, the cucumber is actually doing a bit worse than the tomato.
Also keeping PH under 6.
Might try adding a bit of chelated Iron soon but it seems somewhat under control so I'm not worried anymore.
It's exploding with flowers atm...