nutrient accumulations
when you water your plants you want to see a bit of water draining under the pots before stopping
in your case you dont have anything under the smartpots so i guess you never wet the whole medium .. just the top part
not good
put a cup under each plant and empty it manually after you watered
the plants must never sit in water
even better put those plants on a small grow table and recover the bit of drain in a bucket..