Roots also needs air and waterlogging causes root rot. For this reason a good drainage is important, as well as a little drain at each watering. This ensures that no salts will build up that can cause burnings to the roots.
If you would have too much N in your soil mix you would see so called "clawing" on the leafes and a really dark blueish green. Cloudy, bright parts between the leaf veins tend to indicate a magnesium deficiency or light stress and since you regularly use epsom salt, I think it is light stress.
Increase the distance by 4inch and it should not occur on the newer leaves. Already damaged leaves will not recover in this case. If they have a mag. deficit, it may disappear if it's not too far advanced.
Instead of cactus nutrients you should use a bio-mineral all-in-one fertilizer based on molasses and rock dust.
These fertilizers liven up the substrate, provide much humus formation and promote the formation of useful soil flora. You could use the cactus fertilizer as a kind of PK booster.
You can also use worm castings or compost as top-feeding and just put a 1/2-1" thick layer on the substrate surface.
Compost tea is also a really good fertilizer that will not burn your plants.
Without holes in your pots there is no way to flush them. I recommend to flush when you start to change your nutrient regime to flower circle. This rinses out excess nutrients to better absorb the new nutrients and prevents the above described salting of the substrate.
LED tuning for more darker green/black is absolutely nonsense. Better forget advice from from this guy!
Healthy plants are dark green, if not, they have a problem that you need to solve.
and honestly I think the the soil container has no holes, I've been wondering if I should drill some in the bottom. I checked the moistness of the soil with the pH meter (has a moisture setting) and after I just watered, it seems that the water stays suspended in like a 5in tall disk starting at about 2" from the top of the soil, and then drying out again as I approach the bottom, approx 10" below the concentrated disk. I have a cookie sheet under the metal can to catch any drainage, but I honestly have never seen any and I water using an empty vodka bottle (750mL, about half 1-2x a day).
