Newbie Leaf Issues - Yellow/brown spots, White residue, & Dark Green Vein

I am new to growing (this is my first real time, two small grows before) and running into the beginning of some issues. I am hoping someone here with more experience might be able to help me out!

I have the following medical grow set up:
5.5 - 6.5 ph (not exact, using chemicals to test right now, no meter)
15 gal reservoir, Distilled water (adjusted)
Ebb & flow system, 30 min 4x day
GH Flora Series Nutrients, Mild Growth phase
T12 4 ft. fluorescent, cool white and warm, 4 bulbs about 4 inches from plants
2-3 week old clones, four in one tray

These clones were given to me with unknown issues. I am hoping to take care of issues as they come up, so here are the pictures of the problems so far:

#1 Inherit 1 front
#2 Inherit 1 back
#3 Inherit 2
#4 Inherit 3
#5 Leaf residue 1
#6 Leaf residue 2
#7 Hydroton residue
#8 Yellowing leaf
#9 Whole plant (for fun!)

Questions:

1. I think that most of the inherited issues with the plants, which you can see because those leaves are clipped, are nothing to worry about. A little concerned about #4, the dark green vein. It is only on two leaves of this one plant, and it does not seem to be spreading though.

2. Salt residue? I think I may have a salt residue which you can see in #5 thru #7. It is even on my hydroton which I cleaned so many times before using I almost lost my mind (hot water, bleach diluted water, tubs more of hot water). If it is salt, do I add CalMag+? How much would you recommend?

3. Nutrient burn? I think I may have the start of a nutrient burn. I already diluted with 1 gallon of water yesterday, but it still got worse today. You can see this in pic #8 and on the tip of one of the fingers in #4. Do I need to dilute/flush? Will flushing alone fix this, or must I also dilute the nutrients for awhile?

Any help will be greatly appreciated! I am hoping to learn as much as I can so that I don't waste the massive amount of money I spent on my system!

It's common to see issues with the old growth on clones. It looks good to me. You may have some salt residue in your system, hard to tell from the photos.
The leaves on clones are almost always clipped like that to prevent the plant from transpiring too much water when the roots are not establsihed yet. It also prevents powdery mildew and/or mold from forming when the leaves are transpiring water onto each other. Clones can be started in pretty close quarters to each other, which is why they overlap.
Dark green veins can be a Mg deficiency. Look for the new growth to improve, don't feed it much right now. Use a diluted fertilizer solution until it is well rooted. Keep your Ph adjusted, and your good to go.
A lot of the problems that the mother plant had will show on new cuttings (nutrient deficiencies and toxicities mainly) but are overcome and dissapear as soon as it is started in a new medium and nutrient solution. It will be like a new plant. Unless it has inherent fungus issues, but there's no proof of that yet.
Have fun, keep us posted.

Thank you so much for your quick reply! I thought I might be worrying too much, but I am just learning.

Thank you for the information. Good info since I plan on trying my hand at cloning next grow.

I agree, pic #4 shows a likely magnesium deficiency. As for the white stuff, not sure exactly, so I'm not going to guess.

You might have a fungus like Powdery mildew or Downy mildew. Spore can spread to other plants quickly. A product like seranade will work. Remove plants from grow room, clean grow room to remove left over spores. Then put treated plants back in the grow room. Use it once a week til the problem goes away. Also Pyrethrin fogger Bomb will kill any thing moving.

#7 is just nute salts...

Your flood level should be below the level of the hydroton by at least an inch.

Dont worry about the white buildup.

Thank you all for your help. I think all the problems have cleared up. I didn't do anything but flush and keep following my GH nute schedule.

The white build up does continue to be a problem on some leaves and the hydroton, but a flush every two weeks seems to be keeping it at bay. It isn't a mold because it is more of a build-up and I have not found any bugs so my money is on nute salts like NLXSK1 said.