It is so minor, I would not worry about it, some times trying to cure a imagined imperfection can do more harm than good.
Go easy on the feeding though, little plants need little feeding, and I would suggest half strength as plenty for this sized plants and to have a routine of plain water/plain water/feed/plain water/plain water/feed etc, this should be ample nutrition. Once they have 8-10 nodes go to full strength, keeping with the water/water/feed/water/water/feed routine. This will prevent any nutrient salts building up in the substrate.
Remember too, it is very easy to correct a slight under feeding, but very difficult to rescue a burnt and over fed plant.
Flushing unnecessarily will just harm your plants and any healthy bacteria living in your substrate.
Also, after looking at your diary, you seem to be feeding quite heavily and with fertilizers designed for hydroponics, you should really be using either Canna Coco or Canna Terra and not Canna Aqua, this is designed for a completely different situation and may not be ideal for your set up.
And while I am offering advice, I would suggest next time to fill your pots right up to the top. This will allow three things, 1- more space for roots, which leads to faster and bigger growth, 2- allows your plants to sit higher, where they will receive more light, especially reflected light, 3- more substrate lessens the risk of having nutrient salts building up to toxic levels in the substrate. The pots will take up exactly the same amount of room in your tent anyhow, so you may as well provide maximum opportunity for root growth. Plus, the substrate usually compacts down and sinks a bit, so if your pots are only 80% full, in a week or four, they will be only 70% full, resulting in even less room for root growth. Had the pots been 100% full, you would still have 90% room at flowering time.
Which brings me to my next point, with so many plants, you do not have much time until you go to 12/12, otherwise you are going to end up with a very crowded jungle of growth by having that many plants in pots so small and so close to each other.
Although, if you intend doing the "sea of green" method, this close planting should not pose a real problem.
Hope this helps,......
Organoman.