First feeding questions - dependent on so many things - To Feed or not to feed

I was asked a couple of questions regarding nutrient solutions and when they should be started, but I'm afraid I simply do not have the experience to to answer him so I thought I'd ask here. - EVEN - after doing tons of research, I am still unsure after research since the answer depends on so many things such as media, species, lighting, growth rate, conditions, and so on.

A little info regarding the system and actions taken as well as a couple of pics

Not sure what type of system is being used. He describes it as a cross between hydroponics and aeroponics.

5 gal Bucket system with recycling (pump) reservoir (total 10 gal in system at a time). 6" net pots with 4x4 rockwool cubes. The buckets w/plants never have more than a couple of inches in them at a time and the pump is using a single spray head per bucket to water/feed (can also replace the spray head with a drip ring should 1 choose. The pump runs continually and just recycles everything in the system.

seeds were started -Day 1 planted seed and popped in 16 hours
Day 2 seed transplanted to 4x4 cubes left under dome but opened periodically to air
Day 3 placed in bucket system 25% strength of 20-20-20 miracle grow Total PPM 300 (tap is 150)
Day 4 placed under 400W MH
Day 5 added thrive Alive red per hydro bottle instructions 1st Trues show PPM 325
Day 6 1st Trues full 2nd coming
Day 7 Added Thrive Alive Green, Sugardaddy, Root66 per hydro instructions (1/2) strength Total PPM 400
Day 8 2nd trues show / removed 2 liters of nutrient water - replaced with fresh water - PPM 400
Day 9 2nd Trues full 3rd coming - replaced 2 liter of nutrient solution with fresh water - PPM 400
Day 10 3rd trues up
Day 11 3rd trues up (not full) 4th set nubs can be seen - - added Thrive Alive Green, Sugardaddy, Root66 per hydro instructions
(1/2) strength Total PPM 500 (includes Tap of 150)

Ave PH 6.0 thru entire period (minor ph adj made over long periods, everything added was ph corrected before placing into reservoir). Ave solution temp 75 degrees/ room temp 75 degrees - adding frozen plastic water bottles every 6-8 hours to keep solution at ave temp (ranges from 72 - 80 during that period. Light is on 24/7

At Day 11, roots are already extending beyond the 6" net pots (just a couple strands) and the 4th nubs seen but 3rd set not full yet. It also appears that the color is getting lighter and less green but maybe it's light bleaching or shortage of a nutrient. No direct yellowing of tips but can see the areas between the veins are getting lighter and it appears to be an all-over condition.

Research generally states no vegging nutrients until the 3rd week. Altho this is a general stance and differs from species, grow area, medium, and a host of other things, was wondering (3rd not full and 4th trues nubs showing, roots showing under 6" net pots (couple strands), if it would be wise to begin the veg feeding program. Having only seen the results of deficiencies that were not addressed timely, it's hard to judge. With that said and the status of the plant), should they be starting to be fed their veg feeding nutrients? or wait to see what happens (plants getting lighter or not)?

The next question pertains to changing the nutrient solution. Should the original solution be removed and then clean water flushed thru it (res/pump cleaned) before starting absolutely fresh or just drain and add the new solution? To start, the plan would be to start at X% (300PPM including tap) strength of veg mix (at this stage) and increase gradually or should it be stronger (where PPM was or higher than replaced solution).

thanks

I would run those at 200-250ppm on 0.5x conversion scale, but my tap water is 110ppm. Should be safe with 300ppm if you have roots, but I would leave it there for a good while until they get bigger. You can get a pretty good grapefruit rootball before they will start asking for more in my experience on 300ppm. The cotyledons should have enough food to pop out 2 sets of leaves more or less. With average tap water you can go a little further... either way, if you notice fading it's time for nutes.

There is no need to wash out your system every time you change nutes... just empty it, maybe give it a rinse if you're feeling fancy, and put the new shit in it... obviously if you have slime or something you would want to bleach/etc the system.

thank you for the info

I change the nute solution every two weeks or so in veg and as much as I can in flowering, though once the stretch happens they get unwieldy for me. They're in individual buckets. So probably for the last month I don't change the res. However, they also stop taking nutes the last three weeks or so, so I don't worry about nutes getting out of balance. The biggest issue would be if I had a root problem -- then I would have to change the res to treat that. But I haven't had a problem to date.

I follow the "no nutes for the first 2-3 weeks" rule, then go with 100 ppm per week of life, including my water ppm of 140 or so. So at three weeks, 300ppm, at four weeks, 400ppm, etc., through 8 weeks of veg, then stay at 800 for duration of flowering.