my plants are 2 weeks old and i feed with canna nutrients 2ml aqua A + 2ml aqua B + 2ml rhizotonic + 2.5ml cannazym + 2ml mono CAL + 2 ml mono MAG ( it says 1-2 ml per liter of water ) i have phed my water after adding the nutes on one of the plants it looks like it has some rust ...it looks like calcium deficiency , which is wierd since i give 2 ml of CAL
Looks like the cotyledons are still green. More than likely you are over fertilizing them as they are only 2 weeks old. I would recommend just giving straight water until they use up the stored nutrients that are available already. A good rule of thumb is to introduce feeding after the cotyledon is yellowing and about to be used up. If you over fert, you will create nutrient lock out. Which would make sense if you are giving cal mag and this is occurring. Check out my guide on how to spot cannabis deficiencies.
It looks like that one that's a bit busted up could just be from transplanting. Sometimes that happens - but it's still got a good growing tip and new leaves, so it's now getting what it needs. It will pull through - keep doing what you are.